Belinda Morris talks to renowned and much-admired lapidary John Dyer, one of the speakers at the 2016 Gem-A Conference, about the science and art of gem cutting. 

Did you train as a gemmologist or gem cutter?

I loved gems and business from an early age. I was also home-schooled and one of my parents’ strategies for teaching me was to purchase books on subjects I was interested in, so they bought books on gems and gemmology for me (Gem Identification Made Easy by Antoinette Matlins and Antonio C. Bonanno was one of the first) and that stoked my interest.

At 16 I wanted to start in the gem business and my dad said he would help me out. One thing led to another and we ended up going to Zambia to buy gemstones. We bought rough gems instead of cut ones to get a better deal and when we brought them back we took them to a cutter to have them cut. He did a really bad job on them and charged us a lot of money for it. 

This resulted in us getting mad and buying a faceting machine because, as my father said: “We can do that well, or better, ourselves, and cheaper too!” This all turned out to be a blessing in disguise because it helped us to discover that I love to cut gems. So although the gems we bought on that trip were not super profitable in the end, it started us in the direction of what has now become the focus of our business - high quality and creative gem-cutting. 

I never had any formal training. There were no lapidaries interested in teaching near me that I knew of, and as far as gemmology goes I mainly learned from books and practical experience. I would consider myself a far better cutter than gemmologist, but I do have certain practical, applicable gemmological techniques which help me when purchasing rough. Rough is almost easier to ID than cut gems, because you often still have the crystal habit, visible cleavage planes and more inclusions and other factors to help identify a gem and potential treatments it may have undergone. 

Does the stone influence your design or do you choose the stone based on a particular cutting style that you want to see? 

The shape, colour and clarity of the rough are the main considerations in choosing the cut I am going to do. Usually I buy the best rough I can find and then cut to what I feel is best suited to it. There are times when I don’t buy a piece because I feel the shape and size it could cut would not have good marketable appeal, but other than that I pretty much let the rough dictate to me what it wants to be (that’s within certain limitations of marketability and visual appeal, of course). 

That challenge that each gem represents - trying to bring out its maximum potential - is one of the things I most enjoy about cutting. There are so many considerations that go into it and for the most part all those decisions are made on the fly as I saw and preform (pre-shape) the gem for dopping and faceting or carving. 

What is your favourite stone to work with and do you have a preferred design for it? 

My favourite gem to work with is aquamarine since it comes in reasonably large and clean gems, is easy to polish and has great transparency so it is well suited to a wide variety of different cutting styles. Also, since it isn’t dark, it shows the cut well instead of hiding it like some extra dark gems do. 

There are sometimes cutting styles I prefer for specific gems; those with high dispersion (e.g. zircon) do better with flat faceted cuts than with concave facets or carving, since those tend to reduce the dispersion. Other gems with low dispersion I love to cut with concave facets or carving styles since they can increase the brilliance. It’s all part of the decision making process when deciding what to cut a specific piece or rough into. 

You use many less well-known gemstones, do you find that this increases the public’s awareness of these stones, highlighting how beautiful they can be?

As far as using ‘less well-known’ gems go I find that the market is much more accepting of a wide range of gems than in the past. TV shopping has introduced many strange gem types to a large public audience and a certain percentage of that public has gone on to learn a lot about gems and become educated and sophisticated buyers. This, coupled with how expensive the ‘traditional’ gems have become, has really opened a wide door to the lesser known gems. 

That being said though, most of the gems I cut are still within the parameters of what is familiar to most jewellers - aquamarine, beryl, morganite, citrine, amethyst, ametrine, garnet of all kinds, sapphires, emerald, ruby, peridot, tourmaline (all colours), spinel and zircon make up most of my inventory.

Sometimes I will do a very rare gem, such as bicolour spessartite, phenakite, oligoclase or similar, but they are the exception rather than the rule.

What do you endeavour to reveal in stones? 

Essentially what I am looking to reveal is the full potential for beauty that is in each piece of rough. So much labour goes into the searching for and mining of gem rough that I feel it should be cut in a manner that respects its true rarity and uniqueness. But at the same time some sacrifices of size and weight will need to be made for the gem to achieve its maximum beauty. That is the goal that I aim for. 

What do you look for when selecting a piece of rough? 

When selecting rough I look at the size, shape and clarity of each piece. I also take into account the value of the finished piece because there is a lot of labour involved in our cutting and if the finished value of the gem is too low we will not recoup our labour costs. For that reason there are some pieces of rough that are cool and pretty but I just can’t buy them because they won’t generate a profit. 

Do you travel to mines around the world to procure your own rough or do you often buy at shows? 

I have travelled to various countries in search of gems. My most valuable gem (my wife) is Brazilian from the state of Paraíba so the search has paid off! However, gems are often found in very small quantities and a trip direct to the mines can be a fruitless affair since there might not be any production for months at a time. This often results in my needing to buy from middlemen of some kind. Over the years we have formed relationships with a number of rough suppliers who bring us a variety of rough, that it would have been very hard to have access to on our own. After all, cutting is a time consuming business and if I spent all my time running about after rough I wouldn’t get much cutting done. 

Have you had any major cutting catastrophes? 

Major cutting catastrophes are something you like to put out of your mind, but there have been a number of them over the years. There was the kilo of pink tourmaline rough we heated without grinding clean first and broke almost all of it. There was a bixbite (red beryl) from Utah that cost us thousands of that we hoped to get over a carat’s worth of finished cut stone out of it, but it shattered due to internal stress and we ended up with three very small gems from it. There was the imperial topaz that I was carving and got too hot and broke it in half… and many other gems that have broken during carving, or been chipped or something similar. Over 20 plus years of cutting there are a lot of things like that which happen.

Talk us through the process of one of your famous cuts such as the Super Trillion™. What’s the process of cutting a gem in this way? How long does it take to cut some of your most famous designs?? 

The Super Trillion™ is all flat faceted and is an adaptation of a cut that was explained to me by Chris Remen (now deceased) which over time I tweaked to make a number of improvements to. The result is a semi-traditional looking trillion which I feel is super. Since it has so many facets it is very time-consuming to cut. How long it takes depends completely on the type of material and the size of the gem but it usually takes a day or longer to complete. 

A 26.11 ct Citrine Super Trillion^TM. Photo by John Dyer

Do you have any advice for people who want to take up lapidary? 

To take up lapidary as a hobby, the best thing to do is search for a local lapidary club. Often there will be retired members who will teach cutting for a very reasonable price and this often allows you to avoid the initial relatively high cost of the machinery and supplies. For those who want to make this a profession, I would recommend studying the market to be sure that it is really what they want to do… because it is not the easiest thing to make money at. 

You need to be a skilled cutter (something that often takes five years or more to accomplish) and make large investments in raw materials if you are going to sell your own gems. If you don’t sell your own gems, you are going to need to find a niche market for your cutting services and be very fast if you expect to make money because much of the gem trade is used to Asian pricing on gem cutting and that is hard to compete against until you educate your clientele about the difference in look and quality. That means a lot of outreach and marketing is involved. 

You’ve won many awards for your work; which means the most to you? 

The award that means the most to me is the first place I took recently at the German Award for Jewellery and Precious Stones Idar-Oberstein 2015. This is one of my favourite competitions, but the fact that you have to adhere to a theme makes it more complicated. You might have a perfectly beautiful idea for a gemstone cut, but it must go with the theme to win. The theme in 2015 was ‘Light My Fire’, so I thought that an orange gem would fit well with the idea of fire. With this in mind, I searched through my stock of rough and selected a deep orange citrine, which, once ground clean, was a flame shape. Despite this it was still a challenge to decide what to do with the underside of the gem to make it look like fire. However, an idea came to me to execute a pattern that I had never done or seen before and which required an adaptation of my existing machinery and techniques - the result is a gem with a flame shape, but which also has little flame-shaped internal facets on the back which reflect light individually with varying intensities so that they look like flames shooting upwards as the gem is moved. 

Where do you see yourself going with your talent? What’s next for you in the lapidary world? 

It might not be super romantic, but I guess what I see is gradually improving what I already do and adding new styles and techniques to that. As a result of this I feel that each year our gems are better cut, more beautiful and more saleable. ■   

To view John Dyer's work click here

This article originally appeared in Gems&Jewellery Sept/Oct 2016 / Volume 25 / No. 5 pp. 28-32

Interested in finding out more about gemmology? Sign-up to one of Gem-A's courses or workshops.

If you would like to subscribe to Gems&Jewellery and The Journal of Gemmology please visit Membership.

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Beautiful blue turquoise is one of three birthstones for the month of December (in addition to zircon and tanzanite). It is enriched with real cultural significance that can be traced back thousands of years. Here, we explore the blue shades of turquoise and explain what makes this gemstone so special...

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This article by Guy Lalous ACAM EG digests a technical article from The Journal of Gemmology and discusses the capabilities of Laser Ablation Inductively Coupled Plasma Time-of-Flight Mass Spectrometry (LA-ICP-TOF-MS) compared to conventional Inductively Coupled Plasma Quadrupole Mass Spectrometry (ICP-Q-MS). Potential applications of this new analytical technique are also described.  

Gem testing has evolved into an advanced materials science using sophisticated instrumental technologies for detailed chemical and structural analyses. The chemical analysis of gem materials allows identification of synthetics and treatments. Trace-element analysis is useful to identify the geographical origin of high-end stones. When the origin of a stone has a significant impact on it’s value, the cost associated with this technique may be  justified.

How does LA-ICP-MS work?

 The LA-ICP-MS analysis process can be thought of in two main parts: material sampling i.e. Laser Ablation (LA) and chemical analysis i.e. Inductively Coupled Plasma Mass Spectrometry (ICP-MS). A tiny, nearly invisible ablation pit is caused by the laser, into the girdle of the gemstone. There will be minimal damage as the laser vaporises only a microscopic amount of the sample for analysis. It nebulizes the material and the aerosol produced is transferred in a gas stream to an ICP-MS for elemental and/or isotopic analysis. An ICP-MS combines a high-temperature Inductively Coupled Plasma (ICP) with a Mass Spectrometer (MS).   The ICP is an ionisation source where the energy is supplied by electric currents, which ionises the atoms. These ions are then separated based on their mass-to-charge ratio (m/Q) and detected by the MS.  

What is LA-ICP-MS used for?

LA-ICP-MS is recognised as one of the most important spectrometric techniques and has been used in gemmology for quantitative chemical analysis. It provides data that can be used to create chemical fingerprint diagrams for geographical origin determination.

What is ICP-Q-MS?

There are multiple varieties of ICP-MS instruments, which use different mass-separation schemes in analysis. Of these the ICP-Q-MS, which uses a quadrupole is the most popular. The quadrupole is a mass filter. The quadrupole consists of four cylindrical rods arranged so that the ionised sample travels down the centre. Depending on the electro-magnetic field of the rods, the trajectory of the ionised particles is affected, with selected ionic weights based on the m/Q being filtered out and the ions of interest reaching the MS detector. The ability to filter ions on their m/Q allows ICP-MS to supply isotopic information. Different isotopes of the same element have different masses.

What are the limitations of ICP-Q-MS?

The user of this technique has to define a preselected list of isotopes. Isotopes are sequentially measured one at a time, the ‘limited’ sample volume is divided (segmented) between all measured isotopes, thereby drastically reducing the effective sensitivity if many isotopes are monitored.

What are the capabilities of ICP-TOF-MS?

ICP-TOF-MS is one of the latest and most advanced technologies in the ICP-MS family. Time-Of-Flight (TOF) uses the principle that the ‘flight’ duration for one ion passing through a fixed flight tube is related to its m/Q.  Lighter ions take less time to travel the same distance compared to their heavier counterparts with the same charge, provided they have identical kinetic energy, therefore achieving mass separation. ICP-TOF-MS acquires spectra from the lightest to the heaviest isotopes at a higher speed as well as achieving a better resolving power than conventional Q-MS. It ‘snaps pictures’ of the full and continuous mass spectrum without the need to assign isotopes of interest. Such a spectrum reveals almost the full elemental composition, reaping the benefits of the robust plasma source and there is no need to re-ablate the stone due to an incomplete or ‘badly’ chosen predefined list of isotopes.

What practicalities are there to consider with ICP-TOF-MS?

Due to technical limitations the ICP-TOF-MS model described in this article cannot measure light isotopes while maintaining a high sensitivity for heavy isotopes. It takes two measurements to complete the full elemental analysis from Lithium to Uranium. Limit of detection (LOD) values range from single-digit parts per billion (ppb) for heavy elements to low parts per million (ppm) for light elements. TOF-MS provides better LOD than Q-MS. TOF-MS collects all information in the full mass spectrum with no information loss.

What are the potential applications?

The possibilities of the technique will enhance applications such as trace-element characterisation of gemstones and pearls for origin determination and treatment detection, and will open new research opportunities for age dating, inclusion studies and high-spatial-resolution chemical mapping of gems.

The new instrument is called GemTOF and was installed at SSEF in July 2016. ■  

To find out more information about this exciting technique visit GemTOF

This is a summary of an article that originally appeared in The Journal of Gemmology entitled ‘Simultaneous High Sensitivity Trace-Element and Isotopic Analysis of Gemstones Using Laser Ablation Inductively Coupled Plasma Time-of-Flight Mass Spectrometry’ by Hao A.O. Wang, Michael S. Krzemnicki, Jean-Pierre Chalain, Pierre Lefèvre, Wei Zhou and Laurent E. Cartier 2016 / Volume 35 / No. 3 pp. 212-222

Interested in finding out more about gemmology? Sign-up to one of Gem-A's courses or workshops.

If you would like to subscribe to Gems&Jewellery and The Journal of Gemmology please visit Membership.

---

The Fascinating History of Antique Turquoise Jewellery

In his third Gemstone Conversations column for Gems&Jewellery, Jewellery Historian and Valuer John Benjamin FGA DGA FIRV explores the fascinating history of turquoise and its use in jewellery design from the Shahs of Persia to the Art Deco design movement.

Read more

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If you're lucky enough to be born in January, vibrant garnet is your birthstone. A rainbow jewel of the gem world, garnet displays the greatest variety of colour of any mineral and is very often untreated, making it a rarity in the gem world. 

Read more

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Do you know your calcite inclusions from your dumortierite, epidote, fluorite and rutile? Here, Charles Bexfield FGA DGA EG explores some incredible quartz inclusions and explains what to look for when shopping for quartz specimens.

Read more

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Iridescence has to be one of the most mesmerising and magical optical effects seen in gemstones. But have you ever wondered how it occurs? Gem-A's Collection Curator Barbara Kolator FGA DGA shines a light on this fascinating optical effect and tells us about the gems that are most likely to display it.

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Birthstone Guide: Turquoise For Those Born In December

Beautiful blue turquoise is one of three birthstones for the month of December (in addition to zircon and tanzanite). It is enriched with real cultural significance that can be traced back thousands of years. Here, we explore the blue shades of turquoise and explain what makes this gemstone so special...

Read more

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Understanding the Cat's Eye Effect in Gemstones

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The Gem-A Conference is always the highlight of our gemmological calendar! If you didn’t manage to make it, we’ve put together a few of the highlights from this year’s event to fill you in on what you missed, and whet your appetite for Gem-A Conference 2020!

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Award-winning photographer Danny Sanchez GG, a speaker at the 2016 Gem-A Conference, reveals the secrets of photomicrography, the equipment he swears by and his favourite gemstones to photograph.

Q. What drew you towards photomicrography?

I was a working musician in Los Angeles and wanted a change of pace. I’d always loved gems and minerals and when I discovered that you could study them, their origins and applications, at the Gemological Institute of America, I couldn’t enrol quickly enough. The day I opened the course material and saw an inclusion photomicrograph, I was hooked.  

Q. What special equipment do you use?

I might be a little biased so I feel like a lot of my equipment is special. I think my most unusual piece of equipment is a vertical stepping rig that moves the microscope mere microns at a time.  

Q. Can you explain stacking for those that don’t know?

Microscopy deals in very narrow focal planes. A single photo has very little that is actually ‘in focus’. Focus stacking is a technique that allows one to merge multiple photos, each with different focal planes, into a single photo with greater depth of field. This is stacking. Using this technique, one is able to ‘manufacture’ depth. There is definitely a way to overuse stacking. Besides the visual residue that can be found in some photo ‘stacks’ (a group of photos merged into one), if a photo is rendered with too much depth, the viewer can lose perspective. Simply put, but somewhat counterintuitively, a photo with too much depth can look flat. 

Left: A single photomicrograph play of colour in opal from Jalisco, Mexico. Field of view 3.05 mm. Right: The complete stack of 81 photos. Field of view 3.05 mm

Q. Do you look at images from earlier and wish you could retake some of the spectacular ones to add the ‘dimension’ it offers?

I definitely understand the impulse to go back and re-do a shot, but it’s not a strong one for me. I’m always trying to look forward, and to reproduce or re-tool an image I’ve already made seems like a step backward — particularly in light of how many dynamic subjects this industry offers. (For more information on stacking see Prince, N., ‘Use of Stacking Software for Expanding Depth-of-Field in Inclusion Photomicrography’, The Journal of Gemmology, 2014, 34(3), 188–89).  

Q. Do you have any advice for gemmologists wishing to try photomicrography at home?  

There are an overwhelming number of details to consider when trying to take a successful photograph through the microscope, and it’s hard to see the forest for the trees. The simplest recommendation I can make is: buy more light than is necessary. Gemmologists are used to using a specific type and amount of light during observation and imagine that will be sufficient when they sit down to take a photograph. It never is. Light is everything in photography; it’s even more important in photomicrography.  

Q. Do you have any particular favourite inclusions or gemstones to photograph?  

This past year I’ve immersed myself in opal with matrix. I have yet to find a mineral more dynamic that so readily yields actual landscapes. Part of what I look for in my own work is the feeling of being transported somewhere ‘other’. I enjoy the challenge of finding that in quartz or corundum, but when I work with opal in matrix, it’s almost like the photo takes itself.   

Q. How do the public react to your photos? 

Most (non-gemmological) people don’t know what they’re looking at when standing in front of my photos. Once I tell them that it’s a photo of the inside of a gemstone, more often than not, they don’t believe me. Finally, when they do, they have a million questions. It’s really great to see people so invigorated about gems and minerals. I’m sure they’re much more interested when they leave than before they arrived. 

Q. How do you source the stones that you work with? 

Mostly, I’ll buy at trade shows, looking through dealers’ back stock inventory — stones that, for one reason or another, have been passed over. Part of the joy of my process is these little discoveries and bringing something out of them that no one could have imagined. There’s something about owning the stones I work with (and hopefully producing an image from them) that makes the final product that much more satisfying. I’m not sure I can satisfactorily articulate why. Maybe, like every other gemmologist, I just like to hoard stones. 

Q. Do you see your photos as an educational tool or as an art form? 

Art is an inherently selfish act and mine is certainly no exception. All I ever wanted was to capture in my images a sense of mystery and wonder. It is purely self-serving and in this regard, it’s very ‘artsy’. But when people look at my images and discover that they are photos of actual minerals inside other minerals, there is an immediate spark of curiosity. The moment that happens, my photos become educational. 

Q. How long does it take you to capture the ‘magic’ shot? 

I’ll sit down with a parcel of stones and spend hours turning them over in my hands, changing the lighting environment, trying my best to disappear into the process. Once I’ve decided on which stone I’ll pursue, it could take another hour or so to test shoot dozens of lighting environments. The shooting and processing of a stack of 100 or more photos takes another 30 to 40 minutes. The real work happens over the following several days while I digitally develop the photo, just as I would if I were working in a traditional darkroom. 

Q. What’s the most frustrating thing about photomicrography? 

The most frustrating thing is that I can’t do it for a living. My photos don’t have to be perfect, but they have to be representative of the view through my oculars, at the same time capturing the feeling of the moment of discovery. If I don’t feel I’ve done that after I’ve gone through the process of taking the shot(s) and developing the stack, it can be very frustrating. 

Q. What are your future plans for your work? 

Most of my work for the past few years has focused on atmosphere, the space within the stone and not any particular inclusion or the capturing of inclusions. That’s what interests me the most and that’s what I see myself pursuing; capturing and creating the space within gems. 

Q. If fleeing a burning building, what equipment do you grab?

Luckily for me, I’m not a photographer in the traditional sense of the word. I didn’t grow up aspiring to take photos nor did my penchant for gadgetry lean in that direction. My entry into the world of ‘prosumer’ cameras and lenses began with photomicrography. Because of this, I don’t have a collection of lenses or cameras that would make it hard to choose if fleeing a burning building. My most crucial pieces of equipment fit into one small hard case. I’m definitely fortunate in that regard. 

Q. Your studio improvisations suggest you have a good eye for engineering solutions to suit your needs…

Everything I have done, I’ve done on the shoulders of others. Of course, I’d like to think of myself as a tinkerer and problem solver but most of my equipment has existed in some form, on someone else’s desk, in someone else’s setup. It wasn’t easy piecing it all together but with help from a very small handful of people from around the globe, I’ve put together something that I’m really proud of. 

Q. Another big part of the job these days is software; how do you select the software you use? 

I’ve mentioned the stacking software and while that’s a tricky nuanced piece of software, it performs one function and is therefore finite in its ability to affect a photograph. Beyond that there is developing software such as Lightroom and Photoshop. Together, they can be used to alter an image in infinite ways. While they are indispensable tools, I try to remain as faithful to the view through my oculars as possible. 

Q. What are the ‘frontiers’ to be explored in photomicrography? 

I think the frontiers of photomicrography lay in the direction of software. We’re so lucky to be living in a time of amazing advances, in what computers can do to aid in our perception of the world around us. One day I hope to be able to pop on a pair of VR glasses and take a flight through a Kashmir sapphire or Mexican opal. 

Q. Do you have any gemmological heroes? 

Of course, Eduard Gübelin and John Koivula. Without their work, who knows where I’d be. 

Q. Who first encouraged you to be a photographer? 

In 2007, a year or so after I bought my first microscope, I was working at a trade show and was introduced to Edward Boehm. I already knew who he was, both in the trade and his family’s importance in gemmology. I shook his hand and told him, with no small amount of youthful hubris, that I was going to be a photomicrographer. He flashed me that great smile and told me to go for it. Every subsequent time I ran into him, he would always ask how it was going and if I’d made any progress with my photos. I was the smallest blip in his periphery but for the next five years he never forgot to ask about my photos. During that time I struggled with the pursuit itself and a lot of self-doubt. It wasn’t until 2013 that I was proud enough of my work to share it with the general public. His polite consideration was such a small gesture but it made me think: if this great gemmologist, grandson of the man who helped pioneer this field, hasn’t forgotten about me and my pursuit, I can’t forget either. ■   

To view more of Danny Sanchez's work click here or visit his Instagram @mineralien

This article originally appeared in Gems&Jewellery May/June 2016 / Volume 25 / No. 3 pp. 10-12

Interested in finding out more about gemmology? Sign-up to one of Gem-A's courses or workshops.

If you would like to subscribe to Gems&Jewellery and The Journal of Gemmology please visit Membership.

Cover image Opal, from Jalisco, Mexico. Field of view 3.05 mm. All images courtesy of Danny Sanchez. 

---

The Fascinating History of Antique Turquoise Jewellery

In his third Gemstone Conversations column for Gems&Jewellery, Jewellery Historian and Valuer John Benjamin FGA DGA FIRV explores the fascinating history of turquoise and its use in jewellery design from the Shahs of Persia to the Art Deco design movement.

Read more

---

Birthstone Guide: Garnet For Those Born In January

If you're lucky enough to be born in January, vibrant garnet is your birthstone. A rainbow jewel of the gem world, garnet displays the greatest variety of colour of any mineral and is very often untreated, making it a rarity in the gem world. 

Read more

---

Getting Started with Quartz Inclusions

Do you know your calcite inclusions from your dumortierite, epidote, fluorite and rutile? Here, Charles Bexfield FGA DGA EG explores some incredible quartz inclusions and explains what to look for when shopping for quartz specimens.

Read more

---

Understanding Iridescence: Opals, Pearls, Moonstones and Fractured Stones

Iridescence has to be one of the most mesmerising and magical optical effects seen in gemstones. But have you ever wondered how it occurs? Gem-A's Collection Curator Barbara Kolator FGA DGA shines a light on this fascinating optical effect and tells us about the gems that are most likely to display it.

Read more

---

Hidden Treasures: Highlights of Gem-A's Gemstones and Minerals Collection

Gem-A Gemmology Tutor Pat Daly FGA DGA offers us a glimpse at some of the more unusual items in Gem-A's Gemstones and Minerals Collection.

Read more

---

Tanzanite: The Contemporary December Birthstone

Are you looking for the perfect festive gift for a December baby? Gem-A tutor Lily Faber FGA DGA EG considers tanzanite – one of three birthstones for December – and shares how this relatively new gemstone compares to its purple and blue-hued rivals.

Read more

---

Birthstone Guide: Turquoise For Those Born In December

Beautiful blue turquoise is one of three birthstones for the month of December (in addition to zircon and tanzanite). It is enriched with real cultural significance that can be traced back thousands of years. Here, we explore the blue shades of turquoise and explain what makes this gemstone so special...

Read more

---

Understanding the Cat's Eye Effect in Gemstones

Chatoyancy is the gemmological name given to the curious optical effect in which a band of light is reflected in cabochon-cut gemstones, creating an appearance similar to light bouncing off a cat's eye. Gem-A's Collection Curator, Barbara Kolator FGA DGA explains chatoyancy and highlights some of the many gems in which it can occur.

Read more

---

Jade and its Importance in China

Jade has long been revered by gem lovers internationally, but nowhere more so than in China. But what is it that makes this gemstone so special? Gem-A's Assistant Gemmology Tutor Dr Juliette Hibou FGA gives us an overview of jade, how to identify it and its significance in Chinese culture.

Read more

---

Highlights of Gem-A Conference 2019

The Gem-A Conference is always the highlight of our gemmological calendar! If you didn’t manage to make it, we’ve put together a few of the highlights from this year’s event to fill you in on what you missed, and whet your appetite for Gem-A Conference 2020!

Read more

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Paua shells are the archetypal New Zealand gem - possibly even better known than its nephrite jade, known as 'greenstone', or Kauri copal, the fossilised resin or sap of the Kauri Tree. Here, Maggie Campbell Pedersen FGA looks to the ocean to learn more about paua shell, how it is farmed and how it is used in jewellery design. 

What are paua?

Paua belong to the large family of molluscs called Haliotidae, of which there are well over 100 species worldwide. Six are found in New Zealand, although only three are common. The most famous and exclusive to New Zealand is the Haliotis iris, known for the beautiful, vibrant colours of the inside surface of the shells. These colours range from striking blues through to aquamarines to greens, with tints of purple and gold. They are influenced by what the animal eats and therefore vary slightly from region to region.

Haliotis are marine gastropods. They carry one shell, and have one large, very muscular foot with which they attach themselves to rocky surfaces (in the case of H. iris the foot has a black outer skin). The name 'Haliotis' derives from the Greek, meaning 'sea ear', and along one side of the shells are small holes for expelling water in the aeration of the gills. The shell is made up of three layers: a very thin outer layer of conchiolin (a tough, insoluble protein secreted by molluscs, forming the organic matrix of the shell), under which is a chalky-looking rough material and beneath that is the coloured nacre (mother-of-pearl).

In common with other molluscs, the layers of calcium carbonate (in the form of calcite and aragonite) and conchiolin that form their shells, are laid down by the molluscs' soft bodies. Haliotis, however, lay down the inner layer of aragonite crystals and conchiolin in a slightly haphazard way, stopping altogether if the water temperature does not suit them. This results in areas where the conchiolin becomes very visible, giving an effect of wavy lines of organic material interspersed with beautifully coloured nacre.

A captive-bred, live mollusc ready to be harvested at a farm in Thailand

Where can paua be found?

Pauas live around the rocky coasts of New Zealand and are found at or below the level of the lowest spring tide, that is, at a depth of between one and 12 metres. Much of the paua used for gem purposes are wild-caught, under licence and to extremely strict quota. They can only be fished by free diving - no scuba is permitted - and only a certain number may be fished at any one time, all of which helps to keep the stocks of paua healthy. Furthermore, they may not be fished unless they measure a minimum of 125 mm at the longest part of the shell, which they usually reach at the age of about six years.

When did paua aquafarming start?

Paua aquaculture started in New Zealand in the 1980s. The captive-bred molluscs can be harvested when they are smaller - at about three years old. They are largely used for food, as the shells are not of quite such a vibrant colour. The outer, chalky surface of farmed paua is also pale blue (as opposed to the pale brown of wild paua), due to their feed. The soft bodies of farmed paua are slightly paler, which is considered more attractive as food - indeed the very black surface of the wild paua's flesh is usually removed before the meat is consumed.

The flesh of the paua is very rich in protein and has been a staple diet of the Maoris, who also used some of the shells in their carvings, almost always to depict eyes. In the large, wooden carvings that adorned Maori ceremonial houses and canoes whole shells were used, and were attached so that the inner, nacreous surface was visible (see below).

Paua shells used as eyes in a traditional Maori carving

How is paua used in jewellery?

The paua shell trade is unusual in that it is found at both ends of the market. It is well known in the form of colourful, whole polished shells, or inexpensive jewellery and trinkets, which are sold as souvenirs in museum shops and other such places. In jewellers' shops can be found the expensive paua shell items, set in precious metals and with gemstones (see below). At the inexpensive end of the market a little paua shell can go a long way when embedded in moulded clear plastic with a black backing, and is sold in great quantities to the tourist trade. It is made up into various designs, often depicting something specific to New Zealand such as a kiwi bird.

A paua shell necklace by Catherine Best Ltd.

When paua shells are sold whole, the outer, chalky-looking surface is removed to reveal the colourful, nacreous surface beneath, and it takes an expert only about 10 minutes to polish a raw shell on a diamond wheel (see main image). The typical pattern of the nacre with its dark, wavy lines of conchiolin is very attractive, and this is revealed when the outer layers of shell are removed. However, the inside surface of the nacre has a much smoother, almost liquid transition of colours, far fewer lines of conchiolin, and is subsequently considered the better material.

It is from there that the best pieces are taken to make jewellery, and is of course the area in which hemispheres of material are placed to produce blister pearls.

How are paua pearls cultured?

These blister pearls, also known as 'blue pearls', first came onto the market around the turn of the millennium.

These round blister pearls, usually referred to as mabés, are mostly produced from wild-caught paua, which are nucleated and treated in much the same way as the oysters in the culture of marine pearls, that is, by suspending them in baskets from lines in areas of clean water and tending them regularly.

The process of inserting the nucleus must be undertaken with utmost care as the smallest incision in the mantle can result in the death of the mollusc - they have no blood-clotting agent and therefore would bleed to death.

Natural paua pearls do exist, but they are always concretions produced by the animal outside the mantle and are inevitably very oddly shaped (see below). The success rate of the pearl production is not high. Only 10% will produce a marketable blister pearl covered with nacre, and only 2% will produce a smooth one of top quality and colour.

A natural paua pearl

Not only must the animals not be injured during the nucleation process, when the mantle is carefully lifted to insert the hemispherical bead underneath, they must then be kept in a stress-free environment for the two to three years it takes to cover the nucleus with nacre and produce a 'blue pearl'.

As with all organics, science alone cannot ensure success. We also have to rely on the assistance and co-operation of a living creature. ■

The full version of this article originally appeared in Gems&Jewellery July/August 2016 / Volume 25 / No. 4 pp. 10-12

Interested in finding out more about gemmology? Sign-up to one of Gem-A's courses or workshops.

If you would like to subscribe to Gems&Jewellery and The Journal of Gemmology please visit Membership.

All photos by Maggie Campbell Pedersen, except where otherwise stated

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The Fascinating History of Antique Turquoise Jewellery

In his third Gemstone Conversations column for Gems&Jewellery, Jewellery Historian and Valuer John Benjamin FGA DGA FIRV explores the fascinating history of turquoise and its use in jewellery design from the Shahs of Persia to the Art Deco design movement.

Read more

---

Birthstone Guide: Garnet For Those Born In January

If you're lucky enough to be born in January, vibrant garnet is your birthstone. A rainbow jewel of the gem world, garnet displays the greatest variety of colour of any mineral and is very often untreated, making it a rarity in the gem world. 

Read more

---

Getting Started with Quartz Inclusions

Do you know your calcite inclusions from your dumortierite, epidote, fluorite and rutile? Here, Charles Bexfield FGA DGA EG explores some incredible quartz inclusions and explains what to look for when shopping for quartz specimens.

Read more

---

Understanding Iridescence: Opals, Pearls, Moonstones and Fractured Stones

Iridescence has to be one of the most mesmerising and magical optical effects seen in gemstones. But have you ever wondered how it occurs? Gem-A's Collection Curator Barbara Kolator FGA DGA shines a light on this fascinating optical effect and tells us about the gems that are most likely to display it.

Read more

---

Hidden Treasures: Highlights of Gem-A's Gemstones and Minerals Collection

Gem-A Gemmology Tutor Pat Daly FGA DGA offers us a glimpse at some of the more unusual items in Gem-A's Gemstones and Minerals Collection.

Read more

---

Tanzanite: The Contemporary December Birthstone

Are you looking for the perfect festive gift for a December baby? Gem-A tutor Lily Faber FGA DGA EG considers tanzanite – one of three birthstones for December – and shares how this relatively new gemstone compares to its purple and blue-hued rivals.

Read more

---

Birthstone Guide: Turquoise For Those Born In December

Beautiful blue turquoise is one of three birthstones for the month of December (in addition to zircon and tanzanite). It is enriched with real cultural significance that can be traced back thousands of years. Here, we explore the blue shades of turquoise and explain what makes this gemstone so special...

Read more

---

Understanding the Cat's Eye Effect in Gemstones

Chatoyancy is the gemmological name given to the curious optical effect in which a band of light is reflected in cabochon-cut gemstones, creating an appearance similar to light bouncing off a cat's eye. Gem-A's Collection Curator, Barbara Kolator FGA DGA explains chatoyancy and highlights some of the many gems in which it can occur.

Read more

---

Jade and its Importance in China

Jade has long been revered by gem lovers internationally, but nowhere more so than in China. But what is it that makes this gemstone so special? Gem-A's Assistant Gemmology Tutor Dr Juliette Hibou FGA gives us an overview of jade, how to identify it and its significance in Chinese culture.

Read more

---

Highlights of Gem-A Conference 2019

The Gem-A Conference is always the highlight of our gemmological calendar! If you didn’t manage to make it, we’ve put together a few of the highlights from this year’s event to fill you in on what you missed, and whet your appetite for Gem-A Conference 2020!

Read more

---

This article by Guy Lalous ACAM EG summarises a technical article from The Journal of Gemmology discussing the identification criteria for early (pre 2009) and current (post 2009) reconstructed amber, based on documented samples at the National Gemstone Testing Center (NGTC) in Beijing.

Newer amber material presents a serious identification challenge for gemmological laboratories. By comparing the structure of reconstructed amber with that of natural amber, is it possible to identify it? 

Read more: Diving into the World of New Zealand Paua Shells

Amber is formed from fossilised tree resin, but may have inclusions of animals, insects, plant debris, minerals, liquids and gases. The fossilisation process involves a progressive oxidation, where the original organic compounds gains oxygen, and polymerisation, which is an addition reaction where two or more molecules join together. This process produces oxygenated hydrocarbons, which are organic compounds made of oxygen, carbon and hydrogen atoms.

What is reconstructed amber?

Reconstructed amber consists of small amber fragments or scraps that have been reformed into larger pieces under heat and pressure. It is commonly manufactured from pieces of Baltic material. According to the process used, two main types of reconstructed amber exist:

Type 1 made without the addition of any substances to the amber fragments.

Type 2 which contains foreign substances (e.g. natural or artificial resins) that are added to make the material more solid and durable.  

What is Baltic amber? 

Baltic amber is fossil resin from coniferous trees. Baltic amber, also called succinate, contains 3-8% succinic acid. It was formed about 44 million years ago and today it is found in forests in Lithuania, Russia and Poland, where it is mined and exported in large quantities. The origin is confirmed by the presence of a ‘Baltic Shoulder’ in the fourier transform infrared spectroscopy (FTIR) spectra. Infra-red (IR) spectroscopy is the most effective scientific method for identifying fossil resins. 

What are the identification features of heated amber?

Heat-enhanced amber contains brownish flow lines. These flow lines result from the oxidation of pre-existing cracks that are healed during enhancement at low temperature and pressure, to solidify the raw material and to help avoid future cracking. The heating process will change the refractive index (RI) and infrared spectral readings. The higher the temperature used, the higher the RI will be, up to a maximum of 1.60. Exposure to greater temperatures may also alter some of the FTIR features: the ~1735 cm⁻¹ absorption band shifts to down to 1716 cm⁻¹, and the ~1157 cm⁻¹ absorption band moves up to 1175 cm⁻¹. The variations in RI and infrared spectra indicate that an amber specimen has been heated, but they do not provide conclusive evidence of reconstruction. 

Read more: Getting to Grips with GemTof Technology

When there is little or no foreign substance present, the FTIR spectra of reconstructed amber looks almost identical to that of natural amber, and additional examinations using a microscope, polariscope and UV lamp should be performed to make the proper identification. Most samples encountered at NGTC are type 1 reconstructed amber.  

What are the identification features of early reconstructed amber? 

Early reconstructed amber involved the use of relatively high temperature and pressure conditions in air. It is relatively easy to identify. The material displays a relatively dark body colour, poor transparency with a muddy-looking interior, and a diagnostic fragmental or mosaic structure (known as ‘blood streak’ in Chinese as it resembles blood vessels). The boundaries between fragments have oxidised (darker) edges that appear translucent brown or red. In addition to this some early-stage reconstructed amber may display uneven surface lustre, due to different hardness characteristics of the partially melted amber fragments.  

A 3-D mosaic structure in early reconstructed amber shows a network of angular boundaries that completely enclose the fragments. Below: By contrast, heat-enhanced amber displays brownish red flow lines that do not interconnect. Magnification 10x

How can you differentiate between natural and reconstructed amber?

Natural amber is amorphous and often shows anomalous double refraction in the polariscope, sometimes displaying snake-like, wavy or patchy extinction patterns. By contrast, early-stage reconstructed amber shows patchy grainy extinction, with clear grain boundaries and often exhibits interference colours. 

Natural amber usually displays even fluorescence, viewed with a UV lamp or in a DiamondView instrument. While darker-coloured early-stage reconstructed amber may not show diagnostic fluorescence, pale-coloured material commonly shows uneven luminescence with a fragmental or granular structure.  

What are the identification features of current-stage reconstructed amber?

Current-stage reconstructed amber is manufactured under relatively higher temperature and pressure in an oxygen-free environment. It is often subjected to post-processing treatments that are designed to conceal identifying features. These include inducing internal and surface cracks (by heating and cooling), polishing with coarse grit to create a matt appearance, darkening the surface colour (by baking), carving complex patterns and applying coloured coatings. Microscopic observation reveals that finer grains are typically used as raw material for current reconstructed amber. Usually showing a more subtle and fine-grained fragmental structure consisting of areas of pale colour are enclosed by dot-like edges. The dark-coloured grain boundaries are nearly absent and can only be seen with careful observation, the ‘blood streak’ structure is not apparent. The post processing treatments obscure the features observed with the polariscope, UV lamp or the DiamondView. 

Above: Viewed with a strong transmitted light source, this opaque reconstructed amber bead exhibits no ‘blood streak’ structure, although the angular fragments are still apparent. Below: Two beads in an amber bracelet consist of natural amber (left) and current reconstructed amber (right) display fuzzy grain boundaries with no ‘blood streak’ structure. The presence of small grains with angular boundaries is the key identification factor for the reconstructed amber bead. Magnification 16x (left) and 12.5x (right)

Conclusion

The most effective method to identify reconstructed amber from natural amber is microscopy, to observe the internal microstructure. The Polariscope and UV Fluorescence are useful auxiliary methods but cannot be used to reliably separate current reconstructed natural amber. ■

This is a summary of an article that originally appeared in The Journal of Gemmology entitled ‘Identification of Reconstructed Amber from Different Periods’ by Haibo Li, Jie Liang, Taijin Lu, Jun Zhang and Jun Zhou 2016/Volume 35/ No. 4 pp. 320-328

Interested in finding out more about gemmology? Sign-up to one of Gem-A's courses or workshops.

If you would like to subscribe to Gems&Jewellery and The Journal of Gemmology please visit Membership.

Cover image Flanky internal cracks, eviddence of post processing heat treatment in current reconstructed amber. All photos by H. Li

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The Fascinating History of Antique Turquoise Jewellery

In his third Gemstone Conversations column for Gems&Jewellery, Jewellery Historian and Valuer John Benjamin FGA DGA FIRV explores the fascinating history of turquoise and its use in jewellery design from the Shahs of Persia to the Art Deco design movement.

Read more

---

Birthstone Guide: Garnet For Those Born In January

If you're lucky enough to be born in January, vibrant garnet is your birthstone. A rainbow jewel of the gem world, garnet displays the greatest variety of colour of any mineral and is very often untreated, making it a rarity in the gem world. 

Read more

---

Getting Started with Quartz Inclusions

Do you know your calcite inclusions from your dumortierite, epidote, fluorite and rutile? Here, Charles Bexfield FGA DGA EG explores some incredible quartz inclusions and explains what to look for when shopping for quartz specimens.

Read more

---

Understanding Iridescence: Opals, Pearls, Moonstones and Fractured Stones

Iridescence has to be one of the most mesmerising and magical optical effects seen in gemstones. But have you ever wondered how it occurs? Gem-A's Collection Curator Barbara Kolator FGA DGA shines a light on this fascinating optical effect and tells us about the gems that are most likely to display it.

Read more

---

Hidden Treasures: Highlights of Gem-A's Gemstones and Minerals Collection

Gem-A Gemmology Tutor Pat Daly FGA DGA offers us a glimpse at some of the more unusual items in Gem-A's Gemstones and Minerals Collection.

Read more

---

Tanzanite: The Contemporary December Birthstone

Are you looking for the perfect festive gift for a December baby? Gem-A tutor Lily Faber FGA DGA EG considers tanzanite – one of three birthstones for December – and shares how this relatively new gemstone compares to its purple and blue-hued rivals.

Read more

---

Birthstone Guide: Turquoise For Those Born In December

Beautiful blue turquoise is one of three birthstones for the month of December (in addition to zircon and tanzanite). It is enriched with real cultural significance that can be traced back thousands of years. Here, we explore the blue shades of turquoise and explain what makes this gemstone so special...

Read more

---

Understanding the Cat's Eye Effect in Gemstones

Chatoyancy is the gemmological name given to the curious optical effect in which a band of light is reflected in cabochon-cut gemstones, creating an appearance similar to light bouncing off a cat's eye. Gem-A's Collection Curator, Barbara Kolator FGA DGA explains chatoyancy and highlights some of the many gems in which it can occur.

Read more

---

Jade and its Importance in China

Jade has long been revered by gem lovers internationally, but nowhere more so than in China. But what is it that makes this gemstone so special? Gem-A's Assistant Gemmology Tutor Dr Juliette Hibou FGA gives us an overview of jade, how to identify it and its significance in Chinese culture.

Read more

---

Highlights of Gem-A Conference 2019

The Gem-A Conference is always the highlight of our gemmological calendar! If you didn’t manage to make it, we’ve put together a few of the highlights from this year’s event to fill you in on what you missed, and whet your appetite for Gem-A Conference 2020!

Read more

---

Claire Mitchell FGA DGA takes a hands-on look at the Oceanview Mine, in the Pala mining district in California, USA.

Oceanview Mine is situated 2.5 miles northeast of Pala, on the northeastern slope of Chief Mountain, a short, scenic drive from Pala, California. Visitors to the area pass through landscapes bedecked with nurseries growing a multitude of produce and plants; turning off the main highway you pass through beautiful orange groves, finally reaching the dirt track which takes you up to the mine. 

Famous mines in this area also include the Tourmaline Queen, famous for its 'blue cap pocket' tourmaline, and Pala Chief Mine, famous for its kunzite. The area has been a source of gem materials since the 1870s; with its most active period being between 1900 and 1922. 

Claim was first made to the Oceanview deposit in 1907 by Frank A. Salmons. Since then, ownership has passed through several hands during its lifetime, and the mine is now owned by Jeff Swanger, who acts as CEO, owner and operator of Oceanview Gem Mine LLC. In its lifetime the mine has produced some of the best morganite specimens ever recovered in North America, as well as exceptional tourmaline and kunzite, with additional minerals of lepidolite, mica, apatite, quartz and feldspars.

Today the Oceanview Mine is the only actively working underground mine in this district. The mine is also open to the public for a fee-for-dig, dump screening - which I gleefully attended in April 2016.

Read more: Last Chance to See the Record-Breaking Foxfire Diamond at the Smithsonian

Two things first struck me when I first arrived: firstly, the amazing view from the top of the site, and secondly the beautiful, perfumed smell of wildflowers in the air.

The set up for the mining experience was simple: there was a large dump pile of material which had been taken out of the mine by excavator, around which the screening equipment was situated.

When I first arrived I was allocated a position and screening equipment, and after a safety briefing I was instructed on the most efficient and proficient technique for screening the material. We were given four hours to work the pile; so using a bucket and small shovel I collected a full bucket and returned to my workstation. Two large wooden heavy wire screens allow you to 'sift' the material - the first screen (with the larger mesh) sits atop the second screen with a smaller mesh.

Material collected from the pile is placed in the top mesh, the smaller material of which then passes through to the second mesh. Any larger pieces in the top mesh are then washed and checked for gem-quality material and discarded or kept as required.

The material in the second screen is then washed and checked for gem-quality material. It is thrilling seeing glimmers of colour or good crystal form.

Read more: Getting to Grips with GemTOF Technology

After four hours of happy and productive sifting, it was time to assess the fruits of the day's labours. These included tourmaline (pink, green and black, or 'schorl'), mica, quartz, garnet and beryl. Sadly I had to leave behind some of the larger pieces such as the tourmalines in matrix due to weight restrictions on my baggage, which, whilst not 'gemmy', were still very interesting pieces.

Visitors can also experience a jeep tour of Chief Mountain, which not only offers some breath-taking views but also allows you to catch a glimpse of the active mine entrance and prospects, as well as views of other famous mines in the area. At the edge of the ridge you can see the Tourmaline Queen Mountain, and in the distance you can just about see other former mine workings. 

There is truly nothing better than digging for gem materials - it's a great visit, for both the experience and for the introduction into the techniques in sorting by this method. I thoroughly recommend this to anyone visiting the area - a bonus is the fantastic weather and beautiful countryside whilst there. ■     

This article originally appeared in Gems&Jewellery July/August 2016 / Volume 25 / No. 4 pp. 14-15

Interested in finding out more about gemmology? Sign-up to one of Gem-A's courses or workshops.

If you would like to subscribe to Gems&Jewellery and The Journal of Gemmology please visit Membership.

Cover Image coloured tourmaline. All photos by Claire Mitchell. 

---

The Fascinating History of Antique Turquoise Jewellery

In his third Gemstone Conversations column for Gems&Jewellery, Jewellery Historian and Valuer John Benjamin FGA DGA FIRV explores the fascinating history of turquoise and its use in jewellery design from the Shahs of Persia to the Art Deco design movement.

Read more

---

Birthstone Guide: Garnet For Those Born In January

If you're lucky enough to be born in January, vibrant garnet is your birthstone. A rainbow jewel of the gem world, garnet displays the greatest variety of colour of any mineral and is very often untreated, making it a rarity in the gem world. 

Read more

---

Getting Started with Quartz Inclusions

Do you know your calcite inclusions from your dumortierite, epidote, fluorite and rutile? Here, Charles Bexfield FGA DGA EG explores some incredible quartz inclusions and explains what to look for when shopping for quartz specimens.

Read more

---

Understanding Iridescence: Opals, Pearls, Moonstones and Fractured Stones

Iridescence has to be one of the most mesmerising and magical optical effects seen in gemstones. But have you ever wondered how it occurs? Gem-A's Collection Curator Barbara Kolator FGA DGA shines a light on this fascinating optical effect and tells us about the gems that are most likely to display it.

Read more

---

Hidden Treasures: Highlights of Gem-A's Gemstones and Minerals Collection

Gem-A Gemmology Tutor Pat Daly FGA DGA offers us a glimpse at some of the more unusual items in Gem-A's Gemstones and Minerals Collection.

Read more

---

Tanzanite: The Contemporary December Birthstone

Are you looking for the perfect festive gift for a December baby? Gem-A tutor Lily Faber FGA DGA EG considers tanzanite – one of three birthstones for December – and shares how this relatively new gemstone compares to its purple and blue-hued rivals.

Read more

---

Birthstone Guide: Turquoise For Those Born In December

Beautiful blue turquoise is one of three birthstones for the month of December (in addition to zircon and tanzanite). It is enriched with real cultural significance that can be traced back thousands of years. Here, we explore the blue shades of turquoise and explain what makes this gemstone so special...

Read more

---

Understanding the Cat's Eye Effect in Gemstones

Chatoyancy is the gemmological name given to the curious optical effect in which a band of light is reflected in cabochon-cut gemstones, creating an appearance similar to light bouncing off a cat's eye. Gem-A's Collection Curator, Barbara Kolator FGA DGA explains chatoyancy and highlights some of the many gems in which it can occur.

Read more

---

Jade and its Importance in China

Jade has long been revered by gem lovers internationally, but nowhere more so than in China. But what is it that makes this gemstone so special? Gem-A's Assistant Gemmology Tutor Dr Juliette Hibou FGA gives us an overview of jade, how to identify it and its significance in Chinese culture.

Read more

---

Highlights of Gem-A Conference 2019

The Gem-A Conference is always the highlight of our gemmological calendar! If you didn’t manage to make it, we’ve put together a few of the highlights from this year’s event to fill you in on what you missed, and whet your appetite for Gem-A Conference 2020!

Read more

---

Claire Mitchell FGA DGA talks to Dr Jeffrey Post, chairman of the Department of Mineral Sciences and curator of the National Gem and Mineral Collection at the Smithsonian Institution, about advanced gem testing, the Hope diamond and the importance of donations to the museum.

Q. Moving forward, how important do you feel advanced testing will be?

I think it's getting there - a lot has changed in the last 10-15 years, particularly when you look at the kinds of sophisticated research instruments that the various gem labs have now. These days you’ve got pretty smart scientists out there trying to figure out ways to treat and enhance stones, so it takes pretty smart scientists and good instrumentation to be able to detect these treatments and enhancements. Nowadays there are labs all around the world that are treating stones - sometimes you don't find out about certain treatments until quite a bit later - so we are in an ‘arms race’ of sorts. It's getting to be fairly sophisticated material science - the kinds of techniques that are being applied are ones that are not always easy to detect, and ones that we would never have imagined that could be done. 

Read more: Getting to Grips with GemTOF Technology

I and many others have made the argument for a long time that we need well-trained scientists working in some of these labs, because the nature and sophistication of what is being done is dealing in the scientific. I think it’s a shame that there isn't a really clear path for someone to pursue research in science that will be directly relevant to gems. 

However, GIA - along with a couple of other groups - have tried to get together some funding to hire post-doctorates to work on gem-related projects, and have provided hands-on training to people that have good backgrounds in chemistry, physics and material science. It's clearly a step in the right direction - in the end you get someone who has that scientific background, but who also has some experience working on gem materials and who has been introduced to the gem world.

I think that the gem industry has some responsibility to try to help fund more of the kinds of research that needs to be done, research which will ultimately benefit the industry. Look at beryllium diffusion treatment, for example. That was something that no one ever expected - who would of thought of diffusing beryllium into corundum to change its colour - it's a pretty sophisticated treatment that took some research to figure out and understand, and then to develop a way to identify it. The trade were actually behind on that process by several years before it was finally cracked. 

It should be thought of as a much longer term investment - thinking about the health of the industry. For the good of all of us we need to figure out ways to be sure that we are staying up to date with technology, research and developments in related scientific fields. 

Q. The Smithsonian carried out advanced testing on the Hope diamond. It was reported that the type of instrumentation that was used created a very tiny hole in the diamond - did it? Was it hard to make the decision to test it in that way?

I hate to say it but it did. The key words here are that the hole was very, very, very tiny - if you look at it under a microscope you still can't see it. However, the decision to test in that way wasn't hard, not once I knew what the technique entailed. We had a pretty good understanding of what we were doing, what the test would involve and how the diamond would respond to it. We have a saying at the Smithsonian, that every specimen in the collection is available for research because ultimately, why are we keeping these things if we are not learning from them?

The Hope diamond is a very rare, blue diamond that is a piece of the earth. We use minerals and crystals to learn something about the earth - the Hope diamond has its own story to tell us about how it was formed, where it came from and how it is different from other diamonds, so I think that the fact that we have it in the collection means that it is available for us to study.

Read more: Harrods Unearths 228.31 ct Diamond from its Vaults for Private Sale

It wasn't just me it was a measured and thoroughly assessed decision. All the way through the tests we kept a close eye on things and made sure that it was working the way we thought it would, and so yes, we knocked a few billion atoms out of there, but no one is going to miss those few billion atoms. 

In the end we learned a fair bit of information about the diamond. We got a lot of publicity after we did that experiment and I think part of the reason for that was that people never thought about the Hope diamond as anything other than a ‘cursed’ gemstone worth a lot of money, so I think for many it was an eye-opener to think of it as something that is worth studying. The fact that it stays in the collection means that we can continue studying it.  

The instrument we use is the Time-of-Flight Secondary Ion Mass Spectrometer (ToF-SIMS) - 10-15 years ago we would never have imagined being able to use such an instrument or for somebody to have one in their department, so who knows, 10-15 years from now what other instrumentation will come along? What other options for testing will we have access to, that are equally non-destructive? It's therefore nice to know that we can go back and continue to try and pull a few little pieces of information from the item and continue to learn its secrets.  

Q. How important is the private sector to the purchase of acquisitions?

It's absolutely critical as the Smithsonian is a public-private partnership. We end up depending very heavily on private donations, particularly endowments that people have set up. Some of these go back 100 years whilst some of them are more recent, so one of our goals is that we are always trying to build up our endowments to continue to support the work that we do. 

Typically the collection has grown not from what we have purchased but from what people have given, so the big private partnerships are the donations that people have given us to help build the collection. Sometimes they come in as a large collection of minerals, sometimes as a single piece of jewellery or a single gemstone. The Smithsonian has been around for a long time (by USA standards, anyway) and so if we continue to accumulate at a steady rate the collection will grow to an even bigger collection. 

Read more: Last Chance to See the Record-Breaking Foxfire Diamond at the Smithsonian

Luckily we have time on our side; we don't need to get everything right away. One of the great parts of my job is the feeling that you are part of something that has had a long history and will have a long future - it's a cool feeling to be a part of something that has longevity associated with it. It gives you context for the work that you are doing and allows you to relax a little bit and say “I don't need to get that thing this year”, or “I don’t need to sell everything to get that one thing”, because that one thing, even if it goes into another collection now, will still be out there. 

It helps me to realise that my job never really had a beginning and doesn't really have an end; you are just stepping in as a caretaker of sorts, you keep things going and hopefully you will do some good things that will result in the collection growing.

As the National Museum of the USA we don’t charge, and so there really is a sense that people feel like the museum belongs to them - there is no better situation than one where you're saying “it's your museum, it's your collection, here's what we would like to do.” ■

The full version of this article originally appeared in Gems&Jewellery July/August 2016 / Volume 25 / No. 4 pp. 28-33

Interested in finding out more about gemmology? Sign-up to one of Gem-A's courses or workshops.

If you would like to subscribe to Gems&Jewellery and The Journal of Gemmology please visit Membership.

Cover image the Smithsonian's National Museum of Natural History on the National Mall in Washington, D. C. Copyright Smithsonian Institution

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The Fascinating History of Antique Turquoise Jewellery

In his third Gemstone Conversations column for Gems&Jewellery, Jewellery Historian and Valuer John Benjamin FGA DGA FIRV explores the fascinating history of turquoise and its use in jewellery design from the Shahs of Persia to the Art Deco design movement.

Read more

---

Birthstone Guide: Garnet For Those Born In January

If you're lucky enough to be born in January, vibrant garnet is your birthstone. A rainbow jewel of the gem world, garnet displays the greatest variety of colour of any mineral and is very often untreated, making it a rarity in the gem world. 

Read more

---

Getting Started with Quartz Inclusions

Do you know your calcite inclusions from your dumortierite, epidote, fluorite and rutile? Here, Charles Bexfield FGA DGA EG explores some incredible quartz inclusions and explains what to look for when shopping for quartz specimens.

Read more

---

Understanding Iridescence: Opals, Pearls, Moonstones and Fractured Stones

Iridescence has to be one of the most mesmerising and magical optical effects seen in gemstones. But have you ever wondered how it occurs? Gem-A's Collection Curator Barbara Kolator FGA DGA shines a light on this fascinating optical effect and tells us about the gems that are most likely to display it.

Read more

---

Hidden Treasures: Highlights of Gem-A's Gemstones and Minerals Collection

Gem-A Gemmology Tutor Pat Daly FGA DGA offers us a glimpse at some of the more unusual items in Gem-A's Gemstones and Minerals Collection.

Read more

---

Tanzanite: The Contemporary December Birthstone

Are you looking for the perfect festive gift for a December baby? Gem-A tutor Lily Faber FGA DGA EG considers tanzanite – one of three birthstones for December – and shares how this relatively new gemstone compares to its purple and blue-hued rivals.

Read more

---

Birthstone Guide: Turquoise For Those Born In December

Beautiful blue turquoise is one of three birthstones for the month of December (in addition to zircon and tanzanite). It is enriched with real cultural significance that can be traced back thousands of years. Here, we explore the blue shades of turquoise and explain what makes this gemstone so special...

Read more

---

Understanding the Cat's Eye Effect in Gemstones

Chatoyancy is the gemmological name given to the curious optical effect in which a band of light is reflected in cabochon-cut gemstones, creating an appearance similar to light bouncing off a cat's eye. Gem-A's Collection Curator, Barbara Kolator FGA DGA explains chatoyancy and highlights some of the many gems in which it can occur.

Read more

---

Jade and its Importance in China

Jade has long been revered by gem lovers internationally, but nowhere more so than in China. But what is it that makes this gemstone so special? Gem-A's Assistant Gemmology Tutor Dr Juliette Hibou FGA gives us an overview of jade, how to identify it and its significance in Chinese culture.

Read more

---

Highlights of Gem-A Conference 2019

The Gem-A Conference is always the highlight of our gemmological calendar! If you didn’t manage to make it, we’ve put together a few of the highlights from this year’s event to fill you in on what you missed, and whet your appetite for Gem-A Conference 2020!

Read more

---

Sarah Steele FGA DGA discusses the many simulants of one of Britain’s most famous native gemstones, Whitby jet.

If imitation is the sincerest form of flattery, then Whitby jet must be a very desirable material indeed. I can think of perhaps 20-30 different materials, both natural and synthetic, which, at one stage or another over the years, have been described as Whitby jet.

We think of a 40-year period during the mid to late nineteenth century as the heyday in Whitby jet manufacture, and from a jewellery output perspective that is unequivocally true. However, the desire for Whitby jet, and the quest to imitate it, has its roots much further back in time. 

Read more: Reconstructed Amber Broken Down

Following the Scottish Gemmological Association’s Conference this year, delegates had the opportunity to visit the 'Celts' exhibition at The National Museum of Scotland. I couldn’t resist the opportunity to join them in having a closer look at the museum’s stunning collection of Bronze Age jet neckpieces whilst we were there.

Historically, many of these early pieces containing black beads with high organic carbon content were described as Whitby jet. Modern analytical techniques have shown, however, that these almost always contain a variety of materials - Whitby jet, certainly - but also oil shales, lignites and cannel coals, often within the one piece of jewellery. 

Whitby jet is a material with which the demand for rough will always outstrip supply in periods of high production, and jet collection requires patience as it is reliant on coastal erosion. Are we then, in the Bronze Age some 4,500 years ago, seeing the first example of a Whitby jet simulant? It has to be noted that the prevalence of Whitby jet in the archaeological record during this period suggests that it is arguably one of the oldest economic resources in the British Isles.

Fast forward 2,670 years and the Whitby jet simulant market is a fascinating and booming industry. British society is participating in a national obsession with mourning. With the death of George IV in 1830, the Lord Chamberlain’s office dictates the dress code for the period, stating unequivocally that “the ornament shall be jet”. In 1830 the term ‘jet’ meant only one material: Whitby jet. The death of the Duke of Wellington in 1852 prompted the production of Whitby jet jewellery into overdrive - the 50 recorded workshops in 1850 swelled to 204 following the death of Prince Albert in 1861, as yet another wave of mourning swept the nation. 

Read more: From Elizabeth I to Elizabeth Taylor with John Benjamin FGA DGA

Demand for rough Whitby jet was beginning to outstrip supply and other options were needed. The main attraction of Whitby jet as a gem material was of course its deep black colour and liquid-like lustre, but more importantly its low specific gravity (SG) 1.2-1.3. It was fine to look ‘weighed down’ by the convictions of your expression of mourning, but it was practical if the seven strings of beads you wore to denote that you were the seventh daughter of a deceased father, didn’t weigh more than a few ounces.

Therefore, to be a convincing simulant of Whitby jet, the imitation material would need to be light in weight. Whitby jet is also a poor thermal conductor and so always feels warm, as heat is not quickly transferred away from the surface. Today we often describe jet as feeling ‘plasticky’, however, in the mid nineteenth century plastic was yet to be discovered. The simulant therefore needed to be light in weight, black in colour and a poor conductor of heat. 

Horn and tortoiseshell

In 1712 John O’Bisset discovered horn could with the application of heat, be moulded into various shapes. When cooled the shape was retained - O’Bisset had discovered the first natural thermoplastic material. Sheets of horn were put between hot metal plates in a press and pressure applied. Placing the warmed horn into moulds before applying pressure enabled the production of horn boxes, beakers and other items. With the application of black dye, pressed horn was a good candidate for a simulant of Whitby jet and many jewellery items were produced. 

Horn has a tendency to delaminate due to its layered structure, so loupe examination often reveals these layers, especially on the reverse of brooches. Any damage to the edges also gives a slight transparency to the damaged area, which is not seen in Whitby jet. The colour can often seem uneven and it is not possible to screw a brooch fitting into jet. Therefore a screw, often seen in horn, is always a sign of a simulant. 

Top: Pressed horn jewellery items. Below: The reverse of a pressed horn brooch showing lamination and screw fittings

It is also worth mentioning that tortoiseshell, like horn, is also a natural thermoplastic. Tortoiseshell, a much admired decorative material, derives not from a land tortoise but from certain species of marine turtle, principally the relatively small hawksbill. Tortoiseshell is unlikely to be mistaken for jet due to the mottled colour, but the SG and ‘plasticky’ feel are similar.

Bog oak

Whitby jet is a fossilised wood, so perhaps a wood product could also make a suitable simulant. Bog oak is not a specific species, rather a term that indicates wood that has been buried in a peat bog for thousands of years. The extremely low oxygen conditions of the bog protect the wood from normal decay. While the underlying peat provides acidic conditions where iron salts and other minerals react with the tannins in the wood, gradually giving it a distinct dark brown to almost black colour. 

Bog oak occurs in many areas of the United Kingdom but jewellery usually originates from Ireland. It was produced from the early 1800s but became popular in the mid nineteenth century, reflecting the demand for Whitby jet, especially after 1852, when techniques to mass-mould and decorate the material (through the application of hydraulic or heated pressure to the dried wood) were invented. 

Although predominantly used for mourning jewellery as a cheap substitute for Whitby jet, bog oak was also worn to support Irish crafts, with pieces often carved or stamped with Gaelic motifs such as harps or shamrocks - symbols not normally found in mourning jewellery. Concentric rings are usually visible on the reverse of items as blanks were lathe-turned prior to carving. Loupe examination always show the ligneous nature of the wood and the lustre achieved is usually textured and dull.

Vulcanite

In 1839 Charles Goodyear discovered the method of mixing sulphur with rubber to form hardened or vulcanised rubber, called Vulcanite. The proportion of sulphur can be increased or decreased in order to vary the required amount of hardening accordingly. Between 25-50% sulphur gives a hard product with the familiar feel of plastic. There are many Victorian vulcanite objects, but the most common form is an imitation of Whitby jet used widely in the production of brooches, bracelets and necklaces. Vulcanite could be produced in almost any colour, although the predominant colours are black (ebonite) and brown. As a result, vulcanite was by far the most widely-produced Whitby jet simulant. Unlike pressed horn a thermoplastic materials which, if heated again can be re-moulded into a different shape. Vulcanite is a thermoset material which, after moulding becomes brittle and cannot be remoulded. 

Vulcanite can be distinguished from jet relatively easily. If the material has been exposed to light over time it loses its black colour and becomes khaki brown. When rubbed, vulcanite smells strongly of sulphur and brooch pins are usually screwed into position rather than glued. Chain links only show one or two splits depending on the link style as the link can be twisted open and then closed. In comparison in Whitby jet links, where every other link in the chain is cut and glued and will always show two or three cuts depending on the style of link. As vulcanite pieces were often moulded from jet originals the same design is seen regularly and, with experience, can be identified easily. (Please note: the ‘streak’ test on vulcanite will reveal a light brown streak similar to that of hard Whitby jet and so should not be relied on).

Bois durci

In 1855 Francois Charles Le Page secured a French patent for a method of combining blood albumen from slaughterhouses, with wood powder to form a plastic mouldable material he called bois durci. The wood dust (either ebony or rose wood), was mixed with blood, dried and then ground to a fine powder. The powder was placed in a steel mould and steam heated to 150-250°C in a powerful hydraulic press. After half an hour the mould was plunged into cold water. The resulting wood product was an extremely dense, highly polished and resistant thermoset material. 

Le Page is reported to have used the marketing strapline “Anything Whitby Jet could do, bois durci could do cheaper and in brown”. The most common items available in bois durci today are circular plaques showing royalty or statesmen of the time. They are generally brown and often have bois durci stamped on the reverse.

French jet and Vauxhall glass

As far as Whitby jet imitations go French jet, along with vulcanite one of the most common. Glass items were also produced in large quantities during the Whitby jet heyday, primarily faceted black glass beads referred to as French jet. 

Its higher SG, vitreous lustre and glass moulding marks mean it is unlikely to confuse French jet with Whitby jet. However, because many of the designs were so innocuous, finding a nineteenth century piece of French jet and identifying it from a piece of black glass, used all the way through to the 1940s, can be difficult for collectors of the material. 

Vauxhall glass is often referred to as the English version of French jet, however all French jet was not of course produced in France! This thin highly reflective mirror glass was produced by a silvering process. The silvering is often seen on the reverse - either intact or in residual traces.

Spanish jet

Although all the above impacted the Whitby jet industry, it was a natural jet which was finally responsible for the industry decline. By 1870 the Whitby jet industry reached its peak, before catastrophically collapsing. There were undoubtedly a number of reasons. Some blamed the terrific demand, which had outstripped supply and lead to a fall in standards of workmanship, as many workers hadn’t had the basic training. The large number of simulants also cannot have helped, but the final death knell was heralded by the arrival from the continent of Spanish jet. It is hard to estimate how much of this material was imported from Asturias, but it is first documented in 1874 and many tonnes seem to have been available. 

The Spanish jet trade had flourished between seventh and sixteenth centuries, and whilst the Spanish supply undoubtedly had some very good quality rough material, it seems that Whitby imported a rather poor quality jet, often containing pyrite, making it unstable. Finished pieces degraded quickly, cracked and crumbled. As a result, consumer confidence in an already struggling product sector collapsed.

Decline of the industry

In 1889 the Whitby Gazette reported “It would have been better for the Whitby jet Industry, and better for art development, if the Spanish jet trade had never been known in Whitby”. Despite desperate measures to support the Whitby jet industry, such as a quality mark scheme, the industry didn’t recover. The mourning trend was well and truly over. 

In 1915 The Lady described the Whitby jet trade as “A somewhat funereal fetish of fickle fashion”. Poor recognition for the greatest lapidary trend our nation, and perhaps the world has ever seen. 

The beginning of the twentieth century may have heralded the end of the Whitby jet mourning jewellery trend, but it didn’t signal the end of the road for the use of plastics in jewellery. In 1899 we saw the introduction of casein formaldehye; milk curds hardened with formaldehyde giving us such famous trade names as Galilith, and of course in 1907 phenol formaldehye, with wood flour or other filler as powder gives us the trade name Bakerlite. Galilith and Bakerlite were never used to imitate Whitby jet jewellery - by this time (and forgive the pun) you wouldn’t have been seen dead in this outdated material.

It seemed like the end of the road for Whitby jet. The last apprenticed jet worker Joe Lyth died in 1958, and with him died the secrets of the Victorian era. However, the last 30 years or so we have seen a revival in fortunes within the Whitby jet trade. Today there are 11 manufacturers in Whitby town. As mentioned previously, demand for rough Whitby jet is high and patience is required for collection of beach material. This has allowed poor quality materials, primarily Siberian cannel coals and Georgian jet (both often referred to as Gagate) with its poor stability and high porosity to enter the supply chain. 

Georgian jet is becoming increasingly common as finished contemporary style jewellery made by Baltic amber manufacturers, and within the last 12 months as antique style beads from an undisclosed source. Attempts were even made to sell rough to unsuspecting workshops in Whitby. Experienced lapidaries however quickly identified the new foreign imposter. In Whitby we have no issue with Georgian manufactures producing items from their indigenous jet, but lack of disclosure of origin leads to the material being retailed as Whitby jet somewhere along the pipeline.

Nomenclature and appellation of origin is, as always, crucial to price. A good Whitby jet string of Victorian beads is worth £300 upwards, the Georgian imitation probably nearer £20, so caveat emptor!

As a lapidary in Whitby, I know that the Whitby jet trade will, as always fight back against the latest simulants. A true jet to rival the beauty or stability of Whitby jet has yet to be discovered, but it does make me proud to think that for the last 4,500 years Whitby jet has been held with such reverence that many have tried to emulate it. With the desire of the Victorians to find the perfect simulant, Whitby jet was in part perhaps responsible for the birth of the modern plastics industry, and therefore the modern world as we know it. ■

This article originally appeared in Gems&Jewellery May/June 2016 / Volume 25 / No. 3 pp. 16-20

Interested in finding out more about gemmology? Sign-up to one of Gem-A's courses or workshops.

If you would like to subscribe to Gems&Jewellery and The Journal of Gemmology please visit Membership.

Cover image fine Whitby jet cameos including King Oswy and his bride (centre) and Bejamin Disraeli (right). Photo Credits Sarah Steele, except where otherwise stated. 

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The Fascinating History of Antique Turquoise Jewellery

In his third Gemstone Conversations column for Gems&Jewellery, Jewellery Historian and Valuer John Benjamin FGA DGA FIRV explores the fascinating history of turquoise and its use in jewellery design from the Shahs of Persia to the Art Deco design movement.

Read more

---

Birthstone Guide: Garnet For Those Born In January

If you're lucky enough to be born in January, vibrant garnet is your birthstone. A rainbow jewel of the gem world, garnet displays the greatest variety of colour of any mineral and is very often untreated, making it a rarity in the gem world. 

Read more

---

Getting Started with Quartz Inclusions

Do you know your calcite inclusions from your dumortierite, epidote, fluorite and rutile? Here, Charles Bexfield FGA DGA EG explores some incredible quartz inclusions and explains what to look for when shopping for quartz specimens.

Read more

---

Understanding Iridescence: Opals, Pearls, Moonstones and Fractured Stones

Iridescence has to be one of the most mesmerising and magical optical effects seen in gemstones. But have you ever wondered how it occurs? Gem-A's Collection Curator Barbara Kolator FGA DGA shines a light on this fascinating optical effect and tells us about the gems that are most likely to display it.

Read more

---

Hidden Treasures: Highlights of Gem-A's Gemstones and Minerals Collection

Gem-A Gemmology Tutor Pat Daly FGA DGA offers us a glimpse at some of the more unusual items in Gem-A's Gemstones and Minerals Collection.

Read more

---

Tanzanite: The Contemporary December Birthstone

Are you looking for the perfect festive gift for a December baby? Gem-A tutor Lily Faber FGA DGA EG considers tanzanite – one of three birthstones for December – and shares how this relatively new gemstone compares to its purple and blue-hued rivals.

Read more

---

Birthstone Guide: Turquoise For Those Born In December

Beautiful blue turquoise is one of three birthstones for the month of December (in addition to zircon and tanzanite). It is enriched with real cultural significance that can be traced back thousands of years. Here, we explore the blue shades of turquoise and explain what makes this gemstone so special...

Read more

---

Understanding the Cat's Eye Effect in Gemstones

Chatoyancy is the gemmological name given to the curious optical effect in which a band of light is reflected in cabochon-cut gemstones, creating an appearance similar to light bouncing off a cat's eye. Gem-A's Collection Curator, Barbara Kolator FGA DGA explains chatoyancy and highlights some of the many gems in which it can occur.

Read more

---

Jade and its Importance in China

Jade has long been revered by gem lovers internationally, but nowhere more so than in China. But what is it that makes this gemstone so special? Gem-A's Assistant Gemmology Tutor Dr Juliette Hibou FGA gives us an overview of jade, how to identify it and its significance in Chinese culture.

Read more

---

Highlights of Gem-A Conference 2019

The Gem-A Conference is always the highlight of our gemmological calendar! If you didn’t manage to make it, we’ve put together a few of the highlights from this year’s event to fill you in on what you missed, and whet your appetite for Gem-A Conference 2020!

Read more

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Gem-A member Patricia Campion reports on a recent gemmological field trip to Myanmar, highlighting her experiences of gemstone market places, the Myanmar Gems Museum, in Yangon, and seeing mushroom tourmaline for the first time.

On Christmas Day, our group met in Yangon for a gemmological tour of Myanmar organised by Pauline Jamieson for the Scottish Gemmological Association. Just before we left for Myanmar, our plans suffered a fundamental blow with the Government closure of Mogok to all foreigners due to local civil unrest. However, the organisers did a wonderful last minute job of rearranging our itinerary to ensure that we saw and did much to make up for missing out on the famed ruby mines.  

Read more: Gem Central With Gem Dealer Marcus McCallum

Our gem tour proper commenced in Myitkyina (pronounced My-chee-na), which is home to Myanmar's licensed amber markets. Much of the local amber is a distinctive deep red, although a wide spectrum of colour was available. Burmese amber deposits are considerably older than Baltic amber (up to 100 million years old) and the quality and clarity was high, with some very fine specimens containing preserved insects and plants. The market sold a wide variety of jewellery, carvings and beads as well as rough amber.

As is true all over Myanmar, traders were friendly and very pleasant but prices were higher than expected due to the proximity of the Chinese market.

We also visited some interesting local emporia specialising in jade and got our first glimpse at the many and varied hues available, from magnificent, almost translucent imperial jade through the spectrum of greens, greys and lilacs to white jade and almost transparent 'ice' jade.  

Read more: A Quick Guide to the Crown Jewels at the Tower of London

Arriving in Mandalay, we sallied forth into the infamous Mandalay jade market. Moving at speed through the crowded, cramped space where experts trade jade, we were surrounded by frenetic activity making it an unreal but truly exhilarating experience. In the lower octane atmosphere of the surrounding stalls outside the official jade market, pieces of rough jade could be purchased inexpensively.

Next we visited a family run business selling good quality Mogok ruby at reasonable prices. Their stones had received some heat treatment, but were lively and of good colour and devoid of fissure filling or other undesirable treatments. Later we met gem dealers who had travelled from Mogok, offering a large stock of mainly spinel, peridot, ruby and sapphire.

Star ruby and star sapphire were plentiful, with sapphire tones ranging from deep blue through purples and pinks to silvery grey and creamy yellow. While some stones were marred by rather crude cutting or damaged through poor storage (endemic across Myanmar it seems), the variety of colours available in spinel in particular, was superb.   

Read more: Getting to Grips with GemTOF Technology

The Myanmar Gems Museum, in Yangon, afforded us a wonderful overview of the many rich treasures of Myanmar. Emporia housed within the same building yielded deep green peridot and pale but very clean aquamarine as well as the usual spinel, ruby and sapphire. Many of us appreciated the colour zoned or bi-coloured unheated sapphires, considerably paler than the famed Burmese blue, but prices were prohibitive.

Colourful zircons and sizable rutilated topazes were also plentiful. However, the highlight was the discovery of mushroom tourmaline - a remarkable phenomenon which occurs near Mogok. The ones we saw were grey to pale pink in colour and we also managed to unearth wonderfully colourful cross section slices.

Our time in Yangon encompassed visits to the famed Mogok Street, where many gems are traded, and a whistle stop tour of Bogyoke Aung San Market (formerly known as Scott's Market) where we got our first real chance to see Myanmar golden pearls among other treasures. We also got the opportunity to trade ourselves and perching on stools on a street corner we were instantly surrounded by dealers. Their stock was again mainly ruby, spinel and sapphire both rough and polished, plus some wonderful but rather pricey zircons.  

The expertise and insight of our guide, Duncan Baker, meant that we got an unparalleled glimpse into Myanmar's phenomenal world of gems during our trip. As we departed back home we all agreed that if Mogok reopens we will return to this lovely country with its fabulous treasures and wonderful people. ■

Adapted by the author from an article originally written for the Scottish Gemmological Association. 

Interested in finding out more about gemmology? Sign-up to one of Gem-A's courses or workshops.

If you would like to subscribe to Gems&Jewellery and The Journal of Gemmology please visit Membership.

Cover image rough amber samples. Image courtesy of P. Jamieson

---

The Fascinating History of Antique Turquoise Jewellery

In his third Gemstone Conversations column for Gems&Jewellery, Jewellery Historian and Valuer John Benjamin FGA DGA FIRV explores the fascinating history of turquoise and its use in jewellery design from the Shahs of Persia to the Art Deco design movement.

Read more

---

Birthstone Guide: Garnet For Those Born In January

If you're lucky enough to be born in January, vibrant garnet is your birthstone. A rainbow jewel of the gem world, garnet displays the greatest variety of colour of any mineral and is very often untreated, making it a rarity in the gem world. 

Read more

---

Getting Started with Quartz Inclusions

Do you know your calcite inclusions from your dumortierite, epidote, fluorite and rutile? Here, Charles Bexfield FGA DGA EG explores some incredible quartz inclusions and explains what to look for when shopping for quartz specimens.

Read more

---

Understanding Iridescence: Opals, Pearls, Moonstones and Fractured Stones

Iridescence has to be one of the most mesmerising and magical optical effects seen in gemstones. But have you ever wondered how it occurs? Gem-A's Collection Curator Barbara Kolator FGA DGA shines a light on this fascinating optical effect and tells us about the gems that are most likely to display it.

Read more

---

Hidden Treasures: Highlights of Gem-A's Gemstones and Minerals Collection

Gem-A Gemmology Tutor Pat Daly FGA DGA offers us a glimpse at some of the more unusual items in Gem-A's Gemstones and Minerals Collection.

Read more

---

Tanzanite: The Contemporary December Birthstone

Are you looking for the perfect festive gift for a December baby? Gem-A tutor Lily Faber FGA DGA EG considers tanzanite – one of three birthstones for December – and shares how this relatively new gemstone compares to its purple and blue-hued rivals.

Read more

---

Birthstone Guide: Turquoise For Those Born In December

Beautiful blue turquoise is one of three birthstones for the month of December (in addition to zircon and tanzanite). It is enriched with real cultural significance that can be traced back thousands of years. Here, we explore the blue shades of turquoise and explain what makes this gemstone so special...

Read more

---

Understanding the Cat's Eye Effect in Gemstones

Chatoyancy is the gemmological name given to the curious optical effect in which a band of light is reflected in cabochon-cut gemstones, creating an appearance similar to light bouncing off a cat's eye. Gem-A's Collection Curator, Barbara Kolator FGA DGA explains chatoyancy and highlights some of the many gems in which it can occur.

Read more

---

Jade and its Importance in China

Jade has long been revered by gem lovers internationally, but nowhere more so than in China. But what is it that makes this gemstone so special? Gem-A's Assistant Gemmology Tutor Dr Juliette Hibou FGA gives us an overview of jade, how to identify it and its significance in Chinese culture.

Read more

---

Highlights of Gem-A Conference 2019

The Gem-A Conference is always the highlight of our gemmological calendar! If you didn’t manage to make it, we’ve put together a few of the highlights from this year’s event to fill you in on what you missed, and whet your appetite for Gem-A Conference 2020!

Read more

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This article by Guy Lalous ACAM EG summarises a study of the geology, gemmological and physical properties of rubies and pink sapphires from Aappaluttoq, one of the last pristine spots on the planet not far from the arctic circle. 

What is the difference between metamorphism and metasomatism?

When rocks change because of an increase in the pressure and/or temperature of their surroundings, it is called metamorphism. When metamorphism is accompanied by a change in the chemistry of a rock, the rock is said to have been metasomatised. Metasomatism involves changes in mineralogy and structure along with the addition and/or removal of elemental constituents.

What are mafic and ultra-mafic rocks?

Both are igneous rocks. In essence, igneous rocks are formed through the cooling and solidification of magma. Ultramafic rocks are igneous rocks with low silica and gas contents which makes them very fluid. Ultramafic rocks are given names depending on whether they are intrusive or extrusive. Peridotite is the name given to intrusive ultramafic rocks, komatiite is the name given to extrusive ultramafic rocks.

Mafic rocks are mostly composed of pyroxene, calcium-rich plagioclase, and minor amounts of olivine. The mafic magmas are somewhat more viscous than the ultramafic magmas, but they are still fairly fluid. Additionally, they contain somewhat more gas than the ultramafic magmas. Gabbro is the name given to intrusive mafic rocks, whereas basalt is the name given to extrusive mafic rocks.

The corundum from Greenland occurs within a phlogopite-bearing metasomatic rock. The rocks at Aappaluttoq have been subjected to high-pressure, high-temperature metamorphism. The mineralisation at Aappaluttoq is hosted by a reaction zone that formed from metasomatic interactions between ultramafic rock (peridotite) and mafic rock (leucogabbro). The peridotite has low silicon oxide (45 wt.%) and contains various chromophore elements (particularly Chromium, but and also vanadium, iron and titanium). The leucagabbro has an aluminium-rich composition.

During regionals metamorphism, fluid interactions between the two differing rock types created a metasomatic reaction zone encompassing part of the peridotite, the leucogabbro and the contact zone between the two units. Upon regional cooling, the reaction zone formed significant volumes of stable phlogopite with corundum. The availability of chromium from the peridotite allowed the substitution of Cr³⁺ for Al³⁺ in the corundum, producing its pink to red colour.  

Read more: Exploring the wonders of Myanmar

Standard gemmological properties are consistent with metamorphic-metasomatic-type rubies and pink sapphires from other world deposits. Typical inclusion features consist of coarse particles and fine needles of rutile, as well as inclusions of mica, talc, pargasite, cordierite, sillimanite, plagioclase and boehmite. Healed fissures and twinning complete the story. Catapleiite, chlorite, cosalite, dolomite, magnesite, margarite, pyroxene and sapphirine were reported in a previous study.  

A translucent, whitish inclusion of talc commonly observed in rubies and pink sapphires from Greenland. Magnification x58. Image courtesy of C. P. Smith

Spectroscopy in the visible range yielded following data: weak-to-distinct lines were observed at 468 nm and at 475/476 nm along with faint lines at 659 and 668 nm, plus two strong lines at 692 and 694 nm (which appeared as a bright emission line at 693 nm).  

Read more: Reconstructed Amber Broken Down

In the mid-infrared region of the spectrum, some rubies and pink sapphires from Greenland showed distinct bands at approximately 3310 and 3075 cm⁻¹ (and weak bands at approximately 2100 and 1980 cm⁻¹). These features indicate the presence of boehmite, which was mostly concentrated along intersection tubules related to twinning and/or parting planes. Such absorption characteristics are helpful not only for identifying the presence of foreign mineral phases, but also for proving that a gem has not been heated. 

What about origin determination and treatments?

A genuine untreated ruby is increasingly rare and non-treated gems fetch a substantial premium. Proven origins such as Kashmir for sapphires or Mogok for rubies may considerably contribute to the value of a gemstone. The trade is therefore requesting origin determination from gemmological laboratories. It all started with a microscopic approach in the eighties and developed over time as chemical and spectroscopic criteria were introduced.

Crystal growth characteristics, inclusion identification using a Raman microprobe and analytical tools such as Laser Induced Breakdown Spectroscopy (LIBS) and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) have been incorporated into the routine of gemstone analysis.

Consequently, access to chemical elements is gained at very low detection limits. The latest technological development Inductively Coupled Plasma Time-of-Flight Mass Spectrometry (ICP-MS-TOF) allows trace-element characterisation of gemstones for origin determination and treatment detection, is fit for age dating, inclusion studies and high-spatial-resolution chemical mapping of gems.  

Read more: Getting to Grips with GemTof Technology

The chemical composition of the Greenland rubies and pink sapphires is characterised by relatively high iron contents and comparatively low concentrations of titanium, vanadium and gallium. The iron content separates them from the majority of stones from marble-type deposits.

Rubies and pink sapphires from basalt-related deposits also contain relatively high iron, although correlations between other trace elements can help to separate them from those of Greenland. The iron content of our Greenland stones was similar to that of some rubies and pink sapphires from East Africa. Further work on the trace-element and isotopic composition of the Greenlandic material is ongoing and should prove helpful for origin fingerprinting. Certain mineral inclusions such as cordierite, cosalite and catapleiite may point to a Greenland origin.  

Modern mining techniques are planned to maximise production and minimise cost. The mine economics were modelled using only melee-sized rough gem material. Pink sapphire makes up approximately 60-80% of the production, with ruby making up the balance. None of the stones included in the study were heat treated. It should be expected that heated Greenland corundum will become available at some point. The deposit has the potential to make an important contribution to the global supply of ruby and pink sapphire for many years. ■

This is a summary of an article that originally appeared in The Journal of Gemmology entitled ‘Ruby and Pink Sapphire from Aappaluttoq, Greenland’ Christopher P. Smith, Andrew J. Fagan and Bryan Clark 2016/Volume 35/ No. 4 pp. 294-306

Interested in finding out more about gemmology? Sign-up to one of Gem-A's courses or workshops.

If you would like to subscribe to Gems&Jewellery and The Journal of Gemmology please visit Membership.

Cover image partially healed fissures composed of groups of isolated negative crystals. Magnification x55. Image courtesy of C. P. Smith

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The Fascinating History of Antique Turquoise Jewellery

In his third Gemstone Conversations column for Gems&Jewellery, Jewellery Historian and Valuer John Benjamin FGA DGA FIRV explores the fascinating history of turquoise and its use in jewellery design from the Shahs of Persia to the Art Deco design movement.

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Birthstone Guide: Garnet For Those Born In January

If you're lucky enough to be born in January, vibrant garnet is your birthstone. A rainbow jewel of the gem world, garnet displays the greatest variety of colour of any mineral and is very often untreated, making it a rarity in the gem world. 

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Getting Started with Quartz Inclusions

Do you know your calcite inclusions from your dumortierite, epidote, fluorite and rutile? Here, Charles Bexfield FGA DGA EG explores some incredible quartz inclusions and explains what to look for when shopping for quartz specimens.

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Understanding Iridescence: Opals, Pearls, Moonstones and Fractured Stones

Iridescence has to be one of the most mesmerising and magical optical effects seen in gemstones. But have you ever wondered how it occurs? Gem-A's Collection Curator Barbara Kolator FGA DGA shines a light on this fascinating optical effect and tells us about the gems that are most likely to display it.

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Hidden Treasures: Highlights of Gem-A's Gemstones and Minerals Collection

Gem-A Gemmology Tutor Pat Daly FGA DGA offers us a glimpse at some of the more unusual items in Gem-A's Gemstones and Minerals Collection.

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Tanzanite: The Contemporary December Birthstone

Are you looking for the perfect festive gift for a December baby? Gem-A tutor Lily Faber FGA DGA EG considers tanzanite – one of three birthstones for December – and shares how this relatively new gemstone compares to its purple and blue-hued rivals.

Read more

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Birthstone Guide: Turquoise For Those Born In December

Beautiful blue turquoise is one of three birthstones for the month of December (in addition to zircon and tanzanite). It is enriched with real cultural significance that can be traced back thousands of years. Here, we explore the blue shades of turquoise and explain what makes this gemstone so special...

Read more

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Understanding the Cat's Eye Effect in Gemstones

Chatoyancy is the gemmological name given to the curious optical effect in which a band of light is reflected in cabochon-cut gemstones, creating an appearance similar to light bouncing off a cat's eye. Gem-A's Collection Curator, Barbara Kolator FGA DGA explains chatoyancy and highlights some of the many gems in which it can occur.

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Jade and its Importance in China

Jade has long been revered by gem lovers internationally, but nowhere more so than in China. But what is it that makes this gemstone so special? Gem-A's Assistant Gemmology Tutor Dr Juliette Hibou FGA gives us an overview of jade, how to identify it and its significance in Chinese culture.

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Highlights of Gem-A Conference 2019

The Gem-A Conference is always the highlight of our gemmological calendar! If you didn’t manage to make it, we’ve put together a few of the highlights from this year’s event to fill you in on what you missed, and whet your appetite for Gem-A Conference 2020!

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Those born in March are lucky enough to have two birthstones: the beautiful blue of aquamarine and the mysterious red-spotted bloodstone. Here, we delve into the history and mystical properties of aquamarine and why this sky blue gem is said to be a talisman of good luck, fearlessness and protection. 

The blue hues common to this popular stone are fitting considering the Latin translation of aquamarine is 'water of the sea'. Legends describe it as the mermaid's stone, bringing luck to sailors and protecting them from the perils of ocean travel.

In crystal healing, aquamarine is thought to have soothing energy that quells phobias or irrational fears. It is also associated with the throat chakra and is said to help boost the confidence of public speakers.

From a gemmological perspective, aquamarine is a member of the beryl family of gemstones, which also includes emerald, heliodor, morganite and goshenite. Aquamarine is distinguished from these gemstones by its pale blue to bright blue colour, caused by iron in its chemical composition.

Many aquamarines available on the market have been heat treated to enhance their colour. A yellowish, greenish or bluish-green beryl can be heat treated to produce a stable blue colour or irradiated to produce the yellow of heliodor.

Read more: Exploring the wonders of Myanmar 

Aquamarine displays pleochroism, which means its presents multiple shades of colour at once. Untreated aquamarine can be pale blue, bright blue, green and colourless. It has a hardness of 7.5 on the Mohs scale. 

Where is Aquamarine Found?

Aquamarine is mainly found in Africa and Brazil, however, the March birthstone can also be mined in Australia, China, Myanmar, Pakistan, Madagascar, Russia, USA and Sri Lanka. In the 1950s, a famous and historically-significant deposit of aquamarine was found in Minas Gerais, Brazil, and the gemstones recovered became known as Santa Maria Aquamarines. Many gemstones from this location are highly-prized for their unusually deep blue tone. Today, you may come across the term 'Santa Maria' used to describe a particularly lovely blue colour aquamarine. 

Distinguishing Features of Aquamarine 

Aquamarine often occurs as hexagonal-shaped long prismatic crystals, with striations and rectangular etch marks occasionally found on the prism surfaces. 

Aquamarine's durability and plentiful supply makes it a popular choice among jewellery designers. It can also be fashioned into most cuts, making it a firm favourite with lapidaries. 

Read more: Meet Renowned Gem Cutter John Dyer

Although many cut aquamarines are free of inclusions, two-phase inclusions (liquid and gas filled), spiky cavities, and tubes parallel to the length of the crystal that look like falling rain are common.

The Dom Pedro Aquamarine

Perhaps the most famous aquamarine specimen is the 10,363 ct Dom Pedro, which weighs an astonishing 26 kg. To this day, it holds the title of being the largest piece of aquamarine ever to be cut. It was specialists in Idar-Oberstein, Germany, who took on the challenge in 1992.

Discovered by three Brazilian miners in Pedra Azul, Minas Gerais in Brazil in the late 1980s, the original aquamarine was a metre-long. Accidentally dropped, the specimen fractured into three separate pieces - the Dom Pedro being the largest. 

In 1991, Jürgen Henn from Idar-Oberstein visited the owner of this large aquamarine crystal. In 1992 the stone went on the market and Jürgen asked his colleague Bernd Munsteiner to assess at the stone. Bernd sent his son, Tom Munsteiner and Jürgen’s son, Axel Henn, to strike a deal in Brazil and bring the stone to Germany. 

For a year Bernd worked on the stone, studying the crystal, drawing facet patterns, cutting, faceting and polishing, before transforming the rough stone into an incredible obelisk.

The Dom Pedro first went on public display in 1993 in Basel, Switzerland. Some years later, it was destined to be cut into many smaller stones, but it was rescued by Jane Mitchell, who generously donated the Dom Pedro to the Smithsonian National Museum of History in Washington DC, USA. 

Read more: An Interview with Dr Jeffrey Post of the Smithsonian Institution

This awe-inspiring gemstone is in the permanent collection of the museum, housed in the National Gem Collection Gallery. ■

Interested in finding out more about gemmology? Sign-up to one of Gem-A's courses or workshops.

If you would like to subscribe to Gems&Jewellery and The Journal of Gemmology please visit Membership.

Cover image beryl aquamarine crystal. Photo credit Pat Daly. 

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The Fascinating History of Antique Turquoise Jewellery

In his third Gemstone Conversations column for Gems&Jewellery, Jewellery Historian and Valuer John Benjamin FGA DGA FIRV explores the fascinating history of turquoise and its use in jewellery design from the Shahs of Persia to the Art Deco design movement.

Read more

---

Birthstone Guide: Garnet For Those Born In January

If you're lucky enough to be born in January, vibrant garnet is your birthstone. A rainbow jewel of the gem world, garnet displays the greatest variety of colour of any mineral and is very often untreated, making it a rarity in the gem world. 

Read more

---

Getting Started with Quartz Inclusions

Do you know your calcite inclusions from your dumortierite, epidote, fluorite and rutile? Here, Charles Bexfield FGA DGA EG explores some incredible quartz inclusions and explains what to look for when shopping for quartz specimens.

Read more

---

Understanding Iridescence: Opals, Pearls, Moonstones and Fractured Stones

Iridescence has to be one of the most mesmerising and magical optical effects seen in gemstones. But have you ever wondered how it occurs? Gem-A's Collection Curator Barbara Kolator FGA DGA shines a light on this fascinating optical effect and tells us about the gems that are most likely to display it.

Read more

---

Hidden Treasures: Highlights of Gem-A's Gemstones and Minerals Collection

Gem-A Gemmology Tutor Pat Daly FGA DGA offers us a glimpse at some of the more unusual items in Gem-A's Gemstones and Minerals Collection.

Read more

---

Tanzanite: The Contemporary December Birthstone

Are you looking for the perfect festive gift for a December baby? Gem-A tutor Lily Faber FGA DGA EG considers tanzanite – one of three birthstones for December – and shares how this relatively new gemstone compares to its purple and blue-hued rivals.

Read more

---

Birthstone Guide: Turquoise For Those Born In December

Beautiful blue turquoise is one of three birthstones for the month of December (in addition to zircon and tanzanite). It is enriched with real cultural significance that can be traced back thousands of years. Here, we explore the blue shades of turquoise and explain what makes this gemstone so special...

Read more

---

Understanding the Cat's Eye Effect in Gemstones

Chatoyancy is the gemmological name given to the curious optical effect in which a band of light is reflected in cabochon-cut gemstones, creating an appearance similar to light bouncing off a cat's eye. Gem-A's Collection Curator, Barbara Kolator FGA DGA explains chatoyancy and highlights some of the many gems in which it can occur.

Read more

---

Jade and its Importance in China

Jade has long been revered by gem lovers internationally, but nowhere more so than in China. But what is it that makes this gemstone so special? Gem-A's Assistant Gemmology Tutor Dr Juliette Hibou FGA gives us an overview of jade, how to identify it and its significance in Chinese culture.

Read more

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Highlights of Gem-A Conference 2019

The Gem-A Conference is always the highlight of our gemmological calendar! If you didn’t manage to make it, we’ve put together a few of the highlights from this year’s event to fill you in on what you missed, and whet your appetite for Gem-A Conference 2020!

Read more

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Sarah Steele FGA DGA discusses the unusual history of ancient Preseli bluestone. 

If ever there was an unlikely candidate for a gem material then Preseli spotted dolerite, would at least at face value, be it. Over the last five or six years however it has appeared on the market in increasing quantities, both as jewellery and ornamental items, prompting English Heritage and the National Trust to consider unprecedented measures in order to restrict its sale, leading to an ethical debate: should this native material, which has been important to the occupants of the British Isles since 2900 BC, be available for our general consumption or removed from the market to protect the suggested source of the raw material? 

It seems that the people of the twenty-first century have a desire to own a piece of the material, which has almost come to represent the Stone Age, a material of such importance to our Neolithic ancestors that they engaged in a seemingly impossible feat of human engineering, moving huge blocks of this material 250 miles in order to build one of the world’s most iconic ancient monuments - Stonehenge. 

Stonehenge

Stonehenge, on Salisbury Plain, Wiltshire has been a designated a UNESCO World Heritage Site since 1986, ranking alongside sites such as Machu Picchu in Peru and the Xian Terracotta Warriors in China. 

It is a complex site, best known for the standing stones - the collective landscape of which, in association with other surrounding structures, demonstrates Neolithic and Bronze Age ceremonial and mortuary practices resulting from around 2,000 years of continuous use between 3700-1600 BC. The sheer size of its megaliths, the sophistication of its concentric plan and architectural design, the shaping of the stones and the precision with which it was built, secures Stonehenge as one of the most impressive prehistoric megalithic monuments in the world. 

The large stones that form the Outer Circle are known as ‘sarsens’. They are hard, resistant sandstones thought to have been collected from glacial moraine deposited within the local Salisbury Plain environment. The sources of the smaller stones that form the Inner Circle and the Inner Horseshoe, known as the ‘bluestones’, are not native to the Salisbury Plain area. 

Read more: Whitby Jet, A Discussion of its Simulants

The earliest structures known in the immediate area are four or five pits, three of which appear to have held large pine totem-pole-like posts erected in the Mesolithic period, between 8500 and 7000 BC. It is not known how these posts relate to the later monument of Stonehenge but we do know that in about 2900 BC the bluestones were set up in the centre of the monument. 

Perhaps the distance over which these bluestones have been transported is the cause of man’s fascination with them, instead of the larger sarsen stones. This was addressed in 1923 by H. H. Thomas from the Geological Survey, who published a paper in The Antiquaries Journal claiming that he had “sourced the spotted dolerite component of the bluestones in hilltop rock outcrops in the High Preseli, to the west of Crymych in west Wales. Specifically, he thought that the tors on Carn Meini (also known as Carn Menyn) and Cerrig Marchogion were the likely source outcrops” (Earth Heritage, Summer 2013). 

Geology

Preseli bluestone is a metamorphosed dolerite outcropping in the Preseli Hills, known locally as Preseli Mountains, Pembrokeshire Wales. It is particularly notable for its spotted appearance in hand specimen, an effect caused by low-grade regional metamorphism during the Caledonian Orogeny. 

In thin sections the rock contains large pyroxene (augite) and altered plagioclase grains. The original igneous minerals have been partially altered to chlorite and epidote during greenschist grade metamorphism, and although large pyroxene grains remain, almost all the plagioclase has been altered. The remainder of the fine-grained matrix was also altered by metamorphism, although many igneous mineral shapes are evident. Not all of the bluestones standing today at Stonehenge, however, are spotted dolerites. Four of them are ash-flow tuffs, of rhyolitic composition. 

In order to identify the origin of the bluestones, Aberystwyth University has worked to analyse the composition of micron-sized zircon crystals from rhyolite samples from Stonehenge using Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). The technique focuses a very high-power laser beam onto the zircon crystals to ‘ablate’ them - essentially vaporising them. The vapour generated by this process is then analysed in the mass spectrometer, which reveals the chemistry of the zircon crystals. This was the first time zircon chemistry had ever been used to determine the provenance of archaeological material. New research by a team of scientists including researchers from University College London (UCL), University of Manchester, Bournemouth University, University of Southampton, University of Leicester, Amgueddfa Cymru - National Museum Wales and Dyfed Archaeological Trust, presents detailed evidence of prehistoric quarrying in the Preseli Hills in Pembrokeshire, helping to answer long-standing questions about why, when and how Stonehenge was built.

Read more: Getting to Grips with GemTOF Technology

They have identified the outcrop of Carn Goedog as the main source of Stonehenge’s ‘spotted dolerite’ bluestones and the outcrop of Craig Rhos-y-felin as a source for one of the ‘rhyolite’ bluestones. The special formation of the rock, which forms natural pillars at these outcrops, allowed the prehistoric quarry-workers to detach each megalith with minimal effort. Dr Josh Pollard, from the University of Southampton, said: “They only had to insert wooden wedges into the cracks between the pillars and then let the Welsh rain do the rest by swelling the wood to ease each pillar off the rock face. The quarry-workers then lowered the thin pillars onto platforms of earth and stone, a sort of ‘loading bay’ from where the huge stones could be dragged away along trackways leading out of each quarry.” 

Modern Demand

The material which has flooded the market is Preseli spotted dolerite rather than the rhyolitic material. It is fashioned primarily into large cabochons or skulls, spheres, wands and other items evoking pagan symbolisms. The bulk of the material is polished in mainland China, with elaborate carvings being worked in the Netherlands according to my source. 

The bodies that are concerned with protecting the sites of the bluestone are increasingly concerned that illegal extraction of material must be occurring due to the large quantity of material on the market. This has an implication from an archaeological point of view as these ancient sites, believed to be the Neolithic quarries from where the megaliths were extracted, may still hold clues as to Stonehenge’s history and are designated Sites of Special Scientific Interest (SSSI) and are therefore legally protected.

Having spoken to the source of the majority of rough material into the supply chain, however, I am assured that all the material currently on the market has come from his source, a farmland some 500 m outside the boundary of the SSSI. He explained to me that the source of his deposits are glacial erratics, the weathering skins of which have indicated a date of deposition circa 11,000 BC at the end of the last ice age and predating quarrying activity by some 7,000 years. The erratics are dug up from his farmland, usually five to six feet below the surface and then exported for manufacture. 

Despite this, in order to protect the bluestone quarries, it has been proposed that a worldwide ban of the sale of Preseli spotted dolerite may be required. This would be unprecedented for a non-organic gem material and raises the important question of whether (and, indeed, how) such prehistoric stone sources should be protected and conserved in the future. It also demonstrates the need for geologists, archaeologists and manufacturers to work more closely together to ensure a greater transparency regarding the sourcing of our British gem materials.

Why Preseli Bluestone? 

The new discoveries may also help to understand why Stonehenge was built. Professor Parker Pearson and his team believe that the bluestones were erected at Stonehenge around 2900 BC, long before the giant sarsens were put up around 2500 BC. So why did Neolithic man decide to use Preseli bluestone? 

A twelfth-century account of Geoffrey of Monmouth uses the myth of Merlin bringing the stones to Stonehenge and states that the stones had medicinal properties that could be accessed by washing the stones and then pouring the water into baths. The water absorbed the healing virtues of the stones. Even today, folklore in Pembrokeshire suggests that the Preseli bluestones possess healing qualities. There is yet another intriguing (and surprising) aspect to the Preseli bluestones, which is that a relatively high proportion of them (perhaps as much as 10%) have the rare property of being lithophones - ‘musical stones’. That is, they can ring like a bell or gong, or resound like a drum, when struck with a small hammerstone, instead of the dull ‘clunking’ sound rock-on-rock usually makes. 

Read more: The History of Diamonds in Engagement Rings

As gemmologists we seldom use sound when contemplating gemstones, other than the distinctive ‘chink’ of spodumene perhaps, but as a lapidary, sound is important when polishing stones. We are often subconsciously using sound for facet orientation, to listen for surface imperfections and to distinguish different hardnesses of the material we are polishing. 

The fact that lithophones are along the Carn Menyn ridge tends to suggest that sound may indeed have been an important factor in the general location being special to Neolithic people - the sounds from stones were perhaps perceived as emanating from spirit inhabitants of rock and cliff interiors. The underlying reason for the perceived importance or special nature of the bluestones by Neolithic people therefore seems to lie in the idea that Mynydd Preseli was viewed as a sacred land in that era. Could it be that deep within our psyche we still carry a connection with this ancient landscape and the desire for objects made of the bluestones is still strong within us? ■ 

This article originally appeared in Gems&Jewellery Mar/Apr 2016 / Volume 25 / No. 2 pp. 25-27

Interested in finding out more about gemmology? Sign-up to one of Gem-A's courses or workshops.

If you would like to subscribe to Gems&Jewellery and The Journal of Gemmology please visit Membership.

Cover image Stonehenge. All images courtesy of Sarah Steele.   

---

The Fascinating History of Antique Turquoise Jewellery

In his third Gemstone Conversations column for Gems&Jewellery, Jewellery Historian and Valuer John Benjamin FGA DGA FIRV explores the fascinating history of turquoise and its use in jewellery design from the Shahs of Persia to the Art Deco design movement.

Read more

---

Birthstone Guide: Garnet For Those Born In January

If you're lucky enough to be born in January, vibrant garnet is your birthstone. A rainbow jewel of the gem world, garnet displays the greatest variety of colour of any mineral and is very often untreated, making it a rarity in the gem world. 

Read more

---

Getting Started with Quartz Inclusions

Do you know your calcite inclusions from your dumortierite, epidote, fluorite and rutile? Here, Charles Bexfield FGA DGA EG explores some incredible quartz inclusions and explains what to look for when shopping for quartz specimens.

Read more

---

Understanding Iridescence: Opals, Pearls, Moonstones and Fractured Stones

Iridescence has to be one of the most mesmerising and magical optical effects seen in gemstones. But have you ever wondered how it occurs? Gem-A's Collection Curator Barbara Kolator FGA DGA shines a light on this fascinating optical effect and tells us about the gems that are most likely to display it.

Read more

---

Hidden Treasures: Highlights of Gem-A's Gemstones and Minerals Collection

Gem-A Gemmology Tutor Pat Daly FGA DGA offers us a glimpse at some of the more unusual items in Gem-A's Gemstones and Minerals Collection.

Read more

---

Tanzanite: The Contemporary December Birthstone

Are you looking for the perfect festive gift for a December baby? Gem-A tutor Lily Faber FGA DGA EG considers tanzanite – one of three birthstones for December – and shares how this relatively new gemstone compares to its purple and blue-hued rivals.

Read more

---

Birthstone Guide: Turquoise For Those Born In December

Beautiful blue turquoise is one of three birthstones for the month of December (in addition to zircon and tanzanite). It is enriched with real cultural significance that can be traced back thousands of years. Here, we explore the blue shades of turquoise and explain what makes this gemstone so special...

Read more

---

Understanding the Cat's Eye Effect in Gemstones

Chatoyancy is the gemmological name given to the curious optical effect in which a band of light is reflected in cabochon-cut gemstones, creating an appearance similar to light bouncing off a cat's eye. Gem-A's Collection Curator, Barbara Kolator FGA DGA explains chatoyancy and highlights some of the many gems in which it can occur.

Read more

---

Jade and its Importance in China

Jade has long been revered by gem lovers internationally, but nowhere more so than in China. But what is it that makes this gemstone so special? Gem-A's Assistant Gemmology Tutor Dr Juliette Hibou FGA gives us an overview of jade, how to identify it and its significance in Chinese culture.

Read more

---

Highlights of Gem-A Conference 2019

The Gem-A Conference is always the highlight of our gemmological calendar! If you didn’t manage to make it, we’ve put together a few of the highlights from this year’s event to fill you in on what you missed, and whet your appetite for Gem-A Conference 2020!

Read more

---

This article by Guy Lalous ACAM EG summarises a study on the gemmological and physical properties of brown zircon from the Central Highlands of Vietnam, together with its chemical composition, Raman, Fourier Transform Infrared Spectroscopy (FTIR) and Ultraviolet Visible Near InfraRed (UV-Vis-NIR) spectroscopic features. 

Zircon, zirconium silicate (ZrSiO₄) crystallises in the tetragonal system and has a high refractive index (RI), high dispersion, and subadamantine lustre. Zircon can be found in igneous, metamorphic and sedimentary rocks and is particularly common in plutonic rocks.

Are there different types of zircon?

Zircon crystals possess a range of optical and physical properties and can be classified in three types: high, intermediate and low. Zircon is quite unique in this regard. High zircon possesses the full crystal structure, there is little or no damage from radioactive elements. In intermediate zircon the radioactive elements have caused some structural damage and the physical and optical properties are in between low and high. The crystal structure of low zircon has been altered by thousands of years of irradiation from its own trace elements with extensive crystal-structure damage as a result. The optical and physical properties of the latter are lower.

What are rare earth elements?

Rare earth elements (REEs) are a group of 17 metals, comprising of the lanthanide series of elements, in addition to scandium and yttrium, which show similar physical and chemical properties to the lanthanides. The REEs have unique metallurgical, magnetic and luminescent properties. Luminescent properties are useful in gemstone determination. 

Read more: Getting to Grips with GemTof Technology

The original rock type of individual zircon grains can be reliably distinguished by taking a multivariate statistical approach, using a range of trace elements including at least hafnium, uranium, thorium, yttrium and the Heavy-REEs.

What is metamictisation?

Metamictisation of natural zircon results from accumulated radiation damage to the crystal structure caused by radioactive decay of trace amounts of urnaium and thorium, substituting for zircon. The most striking effect of metamictisation is the destruction of anisotropy.

What is the origin of colour in zircon?

In general, the colouration of zircon is affected by its trace-element composition (e.g. transition metals and REEs) and also by radiation damage (e.g. radiation-induced colour centres). Hafnium as well as radioactive elements such as U⁴⁺ and Th⁴⁺ can substitute Zr⁴⁺ in dodecahedral coordination. The resulting radiation damage to the structure results in metamict zircon. The reddish brown colour of Ratanakiri (Cambodian) zircon is thought to be due to the defect center caused by irradiation of uranium and thorium, commonly present as trace elements in its structure.

Gemmological and physical properties of the Vietnamese zircons: 

• Rough
• Prismatic
• Orangey brown to dark reddish brown in colour
• Translucent to transparent crystals
• Weak-to-distinct pleochroism.
• Hydrostatic specific gravity (SG) range from 4.10-4.60.
• Samples were inert to UV radiation

The transparent near-colourless to light-coloured samples showed typical REE-related spectroscopic features. UV-Vis-NIR of the reddish brown zircons showed a continuous increase in absorption toward the UV region, in particular between 400 and 600 nm with a shoulder at around 500 nm. The very light brown and orangey brown have a shoulder of very low intensity.

Microscopic observation of the Vietnamese zircons revealed straight and angular growth zoning. The following inclusions were identified: apatite, hematite, red iron hydroxide and ilmenite. Rare inclusions of baddeleyite, tourmaline and jadeite were reported in a previous  study.

What about Raman spectroscopy and crystallinity of zircons?

The process of metamictisation of zircon greatly influences its Raman spectrum. The crystallinity of zircons can be measured as increasing irregularities of bond-lengths, bond-angles and a general breaking-up of the structure result in changes in wavenumbers and widths of the Raman bands. Full width at half maximum is the width of the Raman spectrum curve measured between those points on the y-axis, which are half the maximum amplitude.

Raman spectra of the Vietnamese zircons showed dominant peaks at 1008;  975; 437; 392; 355; 225; 214 and 202 cm^–1. The strongest bands in the 450-350 cm^–1 range and around 1000 cm^–1 are due to internal vibrations of silicon oxide (SiO₄) tetrahedra. The most intense intra-tetrahedral vibrational band at 1008 cm^–1, is best suited to quantify the degree of metamictisation. Crystalline (high-type) zircon shows a full width at half maximum (FWHM) value of 30 cm^–1. The Raman data of Vietnamese zircon have FWHM values in the 2-3 cm^–1.

Read more: Reconstructed Amber Broken Down

FTIR spectra displayed three sharp, intense bands in the 1100-400 cm^–1 range at 854; 609 and 430 cm^-1. The intense band around 854 cm^–1 (and shoulder at 970 cm^-1) is due to internal stretching vibrations of SiO₄ tetrahedra; this band weakens and broadens in metamict zircon. The band at 609 cm^–1 (due to internal bending vibrations of SiO₄ tetrahedra) and the band at 430 cm^-1 (due to the external or lattice vibration mode) may also weaken and broaden with metamictisation, and they are nearly absent from highly metamict samples. FTIR spectroscopy of the Vietnamese zircon confirms the results of the Raman spectra showing that the samples are well crystallised.

The average chemical composition of the zircons show low contents of non-formula elements. The most abundant chemical substitution was halfnium. The total REE-oxide concentrations were 0.03-0.08 wt%. All the samples contained low amounts of thorium and uranium, and the Th:U ratios are consistent with a magmatic origin (and subsequent transport to the earth’s surface in alkali basalts). Raman and FTIR spectroscopy indicate that the zircons are high type (highly crystalline).

Read more: Exploring the Wonders of Myanmar

Heat treatment of the Vietnamese zircon under oxidising conditions produced a lighter but unstable brownish orange colour in the range of 200-500 °C and a stable pale brown colour after heating to 600 °C, whereas treatment under reducing conditions yielded a blue colour after heating to 800-1000 °C. The zircons turn blue as the small concentration of uranium within the atomic structure undergoes a change in charge. The treated blue colour was stable.

Zircon from the Central Highlands of Vietnam has similar properties and heat-treatment behaviours to those of zircon from Ratanakiri. ■ 

This is a summary of an article that originally appeared in The Journal of Gemmology titled ‘Geology, Gemmological Properties and Preliminary Heat Treatment of Gem-Quality Zircon from the Central Highlands of Vietnam’ by  Le Thi-Thu Huong, Bui Sinh Vuong, Nguyen Thi Minh Thuyet, Nguyen Ngoc Khoi, Somruedee Satitkune, Bhuwadol Wanthanachaisaeng, Wolfgang Hofmeister, Tobias Häger and Christoph Hauzenberger 2016/Volume 35/ No. 4 pp. 308-318 

Interested in finding out more about gemmology? Sign-up to one of Gem-A's courses or workshops.

If you would like to subscribe to Gems&Jewellery and The Journal of Gemmology please visit Membership.

Cover image Vietnamese zircon with an internal feature of opaque hematite and red iron hydroxide (magnified 20x). Image courtesy of N. T. M Thuyet and L. T. T. Huong.

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The Fascinating History of Antique Turquoise Jewellery

In his third Gemstone Conversations column for Gems&Jewellery, Jewellery Historian and Valuer John Benjamin FGA DGA FIRV explores the fascinating history of turquoise and its use in jewellery design from the Shahs of Persia to the Art Deco design movement.

Read more

---

Birthstone Guide: Garnet For Those Born In January

If you're lucky enough to be born in January, vibrant garnet is your birthstone. A rainbow jewel of the gem world, garnet displays the greatest variety of colour of any mineral and is very often untreated, making it a rarity in the gem world. 

Read more

---

Getting Started with Quartz Inclusions

Do you know your calcite inclusions from your dumortierite, epidote, fluorite and rutile? Here, Charles Bexfield FGA DGA EG explores some incredible quartz inclusions and explains what to look for when shopping for quartz specimens.

Read more

---

Understanding Iridescence: Opals, Pearls, Moonstones and Fractured Stones

Iridescence has to be one of the most mesmerising and magical optical effects seen in gemstones. But have you ever wondered how it occurs? Gem-A's Collection Curator Barbara Kolator FGA DGA shines a light on this fascinating optical effect and tells us about the gems that are most likely to display it.

Read more

---

Hidden Treasures: Highlights of Gem-A's Gemstones and Minerals Collection

Gem-A Gemmology Tutor Pat Daly FGA DGA offers us a glimpse at some of the more unusual items in Gem-A's Gemstones and Minerals Collection.

Read more

---

Tanzanite: The Contemporary December Birthstone

Are you looking for the perfect festive gift for a December baby? Gem-A tutor Lily Faber FGA DGA EG considers tanzanite – one of three birthstones for December – and shares how this relatively new gemstone compares to its purple and blue-hued rivals.

Read more

---

Birthstone Guide: Turquoise For Those Born In December

Beautiful blue turquoise is one of three birthstones for the month of December (in addition to zircon and tanzanite). It is enriched with real cultural significance that can be traced back thousands of years. Here, we explore the blue shades of turquoise and explain what makes this gemstone so special...

Read more

---

Understanding the Cat's Eye Effect in Gemstones

Chatoyancy is the gemmological name given to the curious optical effect in which a band of light is reflected in cabochon-cut gemstones, creating an appearance similar to light bouncing off a cat's eye. Gem-A's Collection Curator, Barbara Kolator FGA DGA explains chatoyancy and highlights some of the many gems in which it can occur.

Read more

---

Jade and its Importance in China

Jade has long been revered by gem lovers internationally, but nowhere more so than in China. But what is it that makes this gemstone so special? Gem-A's Assistant Gemmology Tutor Dr Juliette Hibou FGA gives us an overview of jade, how to identify it and its significance in Chinese culture.

Read more

---

Highlights of Gem-A Conference 2019

The Gem-A Conference is always the highlight of our gemmological calendar! If you didn’t manage to make it, we’ve put together a few of the highlights from this year’s event to fill you in on what you missed, and whet your appetite for Gem-A Conference 2020!

Read more

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Everyone knows that lucky April-born souls have been blessed with one of the most prestigious birthstones: diamond. However, there is an alternative birthstone for the month and it's a 'hidden gem'... so to speak! Gem-A Member, Julia Griffith FGA DGA EG explains why rock crystal is worth your time and attention. 

Rock crystal is the purest variety of quartz and is transparent and completely colourless. Its name derives from the Greek term krustallos meaning 'ice' and it is the sister gemstone to colourful varieties of quartz, such as amethyst and citrine. 

What makes rock crystal special?

From across the spectrum of gemstones, only rock crystal offers such a wide variety of attractive inclusions. For this reason, rock crystal has the potential to be one of the most characterful and artistic gemstones for collectors and jewellery lovers alike. 

Many may think of 'inclusions' as flaws, however, when viewing the array of possible features that can be available within this gemstone one may change this opinion. There is rutilated quartz, tourmalinated quartz, fluorite in quartz, hematite in quartz, gilalite in quartz, pyrite in quartz… the list goes on! These different mineral inclusions add further variety to the rock crystal family whilst offering dozens of different looks.

Read more: Navigating Enhanced Versus Natural Lapidary Materials 

Rutile in quartz. Image courtesy of Julia Griffith.

Considering its place in the quartz family of gemstones, rock crystal has a hardness of 7 on the Mohs Scale. It is reasonably durable and stable, which makes it suitable for all kinds of jewellery pieces. It can be fashioned as carvings, cabochons or faceted gems.

Read more: The Historic Significance and Mythology of Amethyst 

An additional bonus with quartz is that it is readily available in larger sizes and at wallet-friendly prices. If you are searching for a statement pendant, beautifully-included rock crystal could be a fantastic option. 

Fluorite in quartz. Image courtesy of Julia Griffith.

The Uses of Rock Crystal

Transparent rock crystal has been used as an imitation of diamond for centuries, due to the fact they are both colourless. Rock crystal will not be as 'firey' as diamond as it does not disperse light to the same degree, however, a well-cut rock crystal can be very brilliant with excellent return of white light.

Faceted rock crystals are still used as diamond imitations today, particularly as 'accent stones' in jewellery. Designers may choose to surround a coloured stone with melee-sized rock crystals rather than diamonds, offering affordable price-points to the consumer whilst giving a similar look.

Quartz Crystal Formation

Quartz is a silica (SiO₂) and is the most abundant mineral on Earth and therefore it is mined in many localities throughout the world. Quartz grows as long prismatic crystals with pyramidal points that can occur as single crystals, clusters and geodes - all of which can be very attractive and are commonly used as display pieces or set within jewellery. The largest single crystal recorded was from Itapore, Brazil and measured over 20 feet in length and weighed over 44 tonnes.

The industrial uses for rock crystal quartz outweigh its use in jewellery. It is used within the manufacture of glass, sand, ceramics, brick and abrasives (to name a few) and it is considered one of the world’s most useful natural materials.

Understanding Synthetic Quartz

Since its successful synthesis in the 1950s, synthetic lab-grown quartz is used extensively for the majority of industrial processes and may also be found within the gem trade as fashioned stones. 

Notably, quartz is used in the mechanism of quartz watches (hence the name) and anyone who sells watches will know that quartz movements keep exceptionally accurate time losing only seconds over the life-time of the battery. This is thanks to quartz’s ability to release regular electronic impulses at precise frequencies.

This rare property, known as piezoelectricity, is utilised within our GPS equipment, telephones and radios as well as in the mechanism, which triggers the airbags in our cars.

It is this property, which is thought to be exploited during crystal healing as the energy held within rock crystal is thought to amplify and channel universal energy. Hopefully, we have managed to change your mind about rock crystal! Why not celebrate April births and special occasions with this underappreciated gemstone instead of the diamond? You may just fall in love with something new. ■

Get started on your gemstone journey with gemmology courses and qualifications from Gem-A. Find out about the Gemmology Foundation and Gemmology Diploma here. 

Do you have a passion for diamonds? Discover the Gem-A Diamond Diploma and Short Courses hereand Short Courses here. 

Cover image Tourmaline in quartz. Image courtesy of Julia Griffith.

This article by Guy Lalous ACAM EG summarises a technical article from The Journal of Gemmology discussing the origin of colour and conditions of formation in violet-to-blue Nuummite from Simiuttat, Greenland. 

Nuummite is an iridescent orthoamphbiole rock found in the Nuuk Distruct in south-west Greenland. It has only been known in the trade since 1983. However, the rock is believed to have been formed in the Late Archean period more than three billion years ago. 

A study published in The Journal investigates the mechanism for the violet-to-blue diffraction colouration of the Simiuttat Nuummite, providing a petrological description of the rock and highlighting the metamorphic pressure-temperature (PT) conditions of its formation. The study concludes that the colour of Nuummite is not due to grain chemical variation, but to the spacing of exsolution lamellae in orthoamphibole.

Some gemstones are formed by microscopic layers of material that are stacked upon one another. When light interacts with the different stacks within the gem material it causes flashes of colour. This is called iridescence, which refers to the scattering and diffraction of light, the iridescent effect is seen in a few gemstones including labradorite, moonstone and Nuummite.  

What is the difference between iridescence and diffraction?

Iridescence happens when light passes through a thin, transparent film with a different refractive index from the surrounding material. Thin-film interference of visible light occurs when light interacts with a lamellar material consisting of fine layers that have different refractive indices (RIs). In diffraction, light waves pass through a grating. Diffraction is caused by the bending, spreading and subsequent overlapping of a wave-front when passing through a tiny opening or openings in an otherwise opaque obstacle. Iridescence is frequently used to describe any diffraction and/or thin-film interference-related colour phenomena, as interference and diffraction in minerals are closely related and often occur together.  

Read more: Reconstructed Amber Broken Down

The RIs measured on a polished slice of Nuummite were 1.650–1.660, with a second shadow edge at approximately 1.54. Hydrostatic specific gravity (SG) measurements were 3.09 ± 0.01. The presence of amphibole-, biotite- and cordierite-rich areas explains the different refractometer readings, with values of about 1.66 being typical for orthoamphibole while the additional shadow edge of 1.54 originated from cordierite.  

Observation of the polished slice with a digital microscope showed laths of orthoamphiboles criss-crossing one another. The crystals displayed blue-to-violet flashes, which were only visible on {210} cleavages. The colours vanished when the crystal was tilted to an angle of 5–15° depending on the tilting axis, indicating a strong geometric control on the colouring phenomenon. The surface topography of the {210} cleavages might act as a diffraction grating that could contribute to the iridescence.  

Polarised microscopy of the thin section revealed a close inter-growth of prismatic orthoamphibole, granular cordierite (with weak pinitisation) and brown, strongly pleochroic biotite flakes. All minerals displayed a random orientation, the correct petrographic name of the investigated Nuummite is biotite-cordierite-anthophyllite granofels.   

What is a granofels?

A granofels is a metamorphic rock with prevailing granular-textured minerals lacking any alignment. The anhydrous mineral assemblages found in granofels are produced at the base of the crust, where the conditions lead to their formation. 

Read more: Gem Central Exploring Ruby Treatments with Julia Griffith FGA DGA EG

Phase diagram calculations show the stability field for the mineral assemblage at temperatures of 505-660°C and pressures below 6.4 kbar. The electron microprobe analysis (EMPA) data of the orthoamphibole crystals from the Nuummite samples plot at 590–600°C (±25°C) in the T–Al^IV solvus diagram of Spear, constraining the minimum metamorphic temperature experienced by the rock.   

What is electron microprobe analysis (EMPA)? 

Electron microprobe analysis is an analytical technique that is used to establish the composition of small areas of a specimen. The method is non-destructive and utilises X-rays excited by an electron beam, incident on a flat surface of the sample. 

What do we know about the solvus diagram of spear?

Solvus thermometry involves phases that form a solid solution at high-T but that 'unmix' into separate phases during cooling. The composition of coexisting minerals with a solvus relationship is an indicator of temperature. Data on mineral assemblages can be obtained through EMPA. The existence of a solvus in the orthoamphiboles between low-Al anthophyllite and high-Al gedrite has been noted by several scientists decades ago. Frank S. Spear (1980) conducted research on orthoamphiboles. His conclusion was that careful declination of the solvus T-X space enables to estimate temperatures in samples where two orthoamphiboles coexist.    

Read more: Zircon from Vietnam: Properties and Heat Treatments

EMPA and Raman spectroscopy classify the orthoamphibole as an Al-rich anthophyllite. Raman spectroscopy of the orthoamphibole showed great similarities to gedrite in the RRUFF database.  

Transmission electron microscopy (TEM) images showed a continuous succession of alternating exsolution lamellae of anthophyllite (wide, dark grey bands) and gedrite (narrow, light grey lamellae), which also were revealed by analytical electron microscopy (AEM) chemical analyses. The exsolution lamellae may have formed during cooling after peak metamorphism, during reheating processes in the course of the intrusion of a granite complex or during later metamorphic overprint.  

What is transmission electron microscopy (TEM)?

TEM operates on the same basic principles as a conventional microscope but uses electrons instead of light. What can be seen with a conventional microscope is limited by the wavelengths of light. The much lower wavelengths of the electrons allow a resolution that is thousand times better than with a light microscope.

What is analytical electron microscopy (AEM)?

AEM refers to the collection of spectroscopic data in TEM based on various signals generated following the inelastic interaction of the incident electron beam with the sample. These signals can be used to identify and quantify the concentration of the elements present in the analysed area, map their distribution in the sample with high spatial resolution (down to 1 nm or better), and even determine their chemical state.

Conclusion

The iridescence of Nuummite is due to the interference of light reflected from sub-microscopic, alternating gedrite and anthophyllite exsolution lamellae. Average spacing of 124-133 nm between the lamellae will generate violet-to-blue diffraction colouration, a previous study indicated an average spacing of 180 nm gives rise to yellow iridescence. 

Acknowledgments

We sincerely thank Rex Guo for donating material for this research. We owe great thanks to Dr Nynke Keulen, Karsten Secher and Peter Appel of the Geological Survey of Denmark and Greenland (Copenhagen, Denmark) for providing information on the occurrence of Nuummite in Greenland. Thanks also to Willi Tschudin (Universität Basel) for preparing the thin section and polishing the slice of Nuummite. Finally, thanks to Anja Schreiber (GFZ Potsdam) for the careful preparation of the TEM slices. The manuscript was considerably improved by the suggestions of three anonymous reviewers. ■ 

This is a summary of an article that originally appeared in The Journal of Gemmology titled ‘Violet-to-Blue ‘Nuummite’ from Simiuttat, Greenland: Origin of Colour Appearance and Conditions of Formation’ by Leander Franz, Tay Thye Sun, Richard Wirth, Christian de Capitani and Loke Hui Ying  2016/Volume 35/ No. 4 pp. 330-339 

Interested in finding out more about gemmology? Sign-up to one of Gem-A's courses or workshops.

If you would like to subscribe to Gems&Jewellery and The Journal of Gemmology please visit Membership.

Cover image Keyence digital microscope image of polished Nummite to show an orthoamphibole prism displaying violet-to-blue colouration. Image courtesy of L. Franz. 

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The Fascinating History of Antique Turquoise Jewellery

In his third Gemstone Conversations column for Gems&Jewellery, Jewellery Historian and Valuer John Benjamin FGA DGA FIRV explores the fascinating history of turquoise and its use in jewellery design from the Shahs of Persia to the Art Deco design movement.

Read more

---

Birthstone Guide: Garnet For Those Born In January

If you're lucky enough to be born in January, vibrant garnet is your birthstone. A rainbow jewel of the gem world, garnet displays the greatest variety of colour of any mineral and is very often untreated, making it a rarity in the gem world. 

Read more

---

Getting Started with Quartz Inclusions

Do you know your calcite inclusions from your dumortierite, epidote, fluorite and rutile? Here, Charles Bexfield FGA DGA EG explores some incredible quartz inclusions and explains what to look for when shopping for quartz specimens.

Read more

---

Understanding Iridescence: Opals, Pearls, Moonstones and Fractured Stones

Iridescence has to be one of the most mesmerising and magical optical effects seen in gemstones. But have you ever wondered how it occurs? Gem-A's Collection Curator Barbara Kolator FGA DGA shines a light on this fascinating optical effect and tells us about the gems that are most likely to display it.

Read more

---

Hidden Treasures: Highlights of Gem-A's Gemstones and Minerals Collection

Gem-A Gemmology Tutor Pat Daly FGA DGA offers us a glimpse at some of the more unusual items in Gem-A's Gemstones and Minerals Collection.

Read more

---

Tanzanite: The Contemporary December Birthstone

Are you looking for the perfect festive gift for a December baby? Gem-A tutor Lily Faber FGA DGA EG considers tanzanite – one of three birthstones for December – and shares how this relatively new gemstone compares to its purple and blue-hued rivals.

Read more

---

Birthstone Guide: Turquoise For Those Born In December

Beautiful blue turquoise is one of three birthstones for the month of December (in addition to zircon and tanzanite). It is enriched with real cultural significance that can be traced back thousands of years. Here, we explore the blue shades of turquoise and explain what makes this gemstone so special...

Read more

---

Understanding the Cat's Eye Effect in Gemstones

Chatoyancy is the gemmological name given to the curious optical effect in which a band of light is reflected in cabochon-cut gemstones, creating an appearance similar to light bouncing off a cat's eye. Gem-A's Collection Curator, Barbara Kolator FGA DGA explains chatoyancy and highlights some of the many gems in which it can occur.

Read more

---

Jade and its Importance in China

Jade has long been revered by gem lovers internationally, but nowhere more so than in China. But what is it that makes this gemstone so special? Gem-A's Assistant Gemmology Tutor Dr Juliette Hibou FGA gives us an overview of jade, how to identify it and its significance in Chinese culture.

Read more

---

Highlights of Gem-A Conference 2019

The Gem-A Conference is always the highlight of our gemmological calendar! If you didn’t manage to make it, we’ve put together a few of the highlights from this year’s event to fill you in on what you missed, and whet your appetite for Gem-A Conference 2020!

Read more

---

Emerald has long been one of the world’s most popular and valuable gemstones. Since the times of the Ancient Egyptians, emeralds have been viewed as tokens of good fortune and harbingers of new beginnings and rebirth.

While emeralds are fascinating from a historical and culture perspective, they are equally exciting for gemmologists, particularly when it comes to characteristic inclusions.

Birthstones Guide: Emerald for those Born in May 

A variety of green beryl, the name 'emerald' is derived from the Greek word smaragdus (meaning green). The green colour of emerald is caused by traces of chromium, but vanadium may also be present in some stones.

Today, emeralds can be found in Colombia, Brazil, India, Pakistan, Siberia, South Africa, Zambia and Zimbabwe.

Read more: The 'Emerald Desert' of Western Australia

The inclusions contained in almost all natural emeralds are very useful in distinguishing them from synthetic emeralds and other green stones. The types of inclusions in some emeralds can offer an indication as to their origin - although this is certainly not a foolproof method.

Typical Emerald Inclusions 

As you examine more emeralds, either during your studies or out in the field, consider the following localities and the typical inclusions and features that material from these regions can present.

Examples of these inclusions can be found in the images below, taken by Gem-A tutor, Pat Daly. 

Three-phase inclusion in emerald. Image courtesy of Pat Daly.

 
Needle-like inclusion. Image courtesy of Pat Daly. 

When combined with other assessments, such as the refractive index and specific gravity, these inclusions can give an indication as to the country of origin. ■

Interested in finding out more about gemmology? Discover our courses and workshops here. 

Cover image needle-like inclusions in emerald. Image courtesy of Pat Daly. 

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The Fascinating History of Antique Turquoise Jewellery

In his third Gemstone Conversations column for Gems&Jewellery, Jewellery Historian and Valuer John Benjamin FGA DGA FIRV explores the fascinating history of turquoise and its use in jewellery design from the Shahs of Persia to the Art Deco design movement.

Read more

---

Birthstone Guide: Garnet For Those Born In January

If you're lucky enough to be born in January, vibrant garnet is your birthstone. A rainbow jewel of the gem world, garnet displays the greatest variety of colour of any mineral and is very often untreated, making it a rarity in the gem world. 

Read more

---

Getting Started with Quartz Inclusions

Do you know your calcite inclusions from your dumortierite, epidote, fluorite and rutile? Here, Charles Bexfield FGA DGA EG explores some incredible quartz inclusions and explains what to look for when shopping for quartz specimens.

Read more

---

Understanding Iridescence: Opals, Pearls, Moonstones and Fractured Stones

Iridescence has to be one of the most mesmerising and magical optical effects seen in gemstones. But have you ever wondered how it occurs? Gem-A's Collection Curator Barbara Kolator FGA DGA shines a light on this fascinating optical effect and tells us about the gems that are most likely to display it.

Read more

---

Hidden Treasures: Highlights of Gem-A's Gemstones and Minerals Collection

Gem-A Gemmology Tutor Pat Daly FGA DGA offers us a glimpse at some of the more unusual items in Gem-A's Gemstones and Minerals Collection.

Read more

---

Tanzanite: The Contemporary December Birthstone

Are you looking for the perfect festive gift for a December baby? Gem-A tutor Lily Faber FGA DGA EG considers tanzanite – one of three birthstones for December – and shares how this relatively new gemstone compares to its purple and blue-hued rivals.

Read more

---

Birthstone Guide: Turquoise For Those Born In December

Beautiful blue turquoise is one of three birthstones for the month of December (in addition to zircon and tanzanite). It is enriched with real cultural significance that can be traced back thousands of years. Here, we explore the blue shades of turquoise and explain what makes this gemstone so special...

Read more

---

Understanding the Cat's Eye Effect in Gemstones

Chatoyancy is the gemmological name given to the curious optical effect in which a band of light is reflected in cabochon-cut gemstones, creating an appearance similar to light bouncing off a cat's eye. Gem-A's Collection Curator, Barbara Kolator FGA DGA explains chatoyancy and highlights some of the many gems in which it can occur.

Read more

---

Jade and its Importance in China

Jade has long been revered by gem lovers internationally, but nowhere more so than in China. But what is it that makes this gemstone so special? Gem-A's Assistant Gemmology Tutor Dr Juliette Hibou FGA gives us an overview of jade, how to identify it and its significance in Chinese culture.

Read more

---

Highlights of Gem-A Conference 2019

The Gem-A Conference is always the highlight of our gemmological calendar! If you didn’t manage to make it, we’ve put together a few of the highlights from this year’s event to fill you in on what you missed, and whet your appetite for Gem-A Conference 2020!

Read more

---

This article by Guy Lalous ACAM EG summarises a technical article from The Journal of Gemmology discussing a giant 12-rayed black star sapphire from Sri Lanka with asterism caused by ilmenite inclusions.

How can we classify solid inclusions?

Solid inclusions are divided into three categories, by time of entrapment: those formed before the host crystal, called protogenetic; solids which arise from the solution from which both they and the host originated, called syngenetic and those formed after the host crystal has finished its growth, epigenetic. 

What is exsolution?

Exsolution in mineralogy is a process where an initially homogeneous solid solution separates into at least two different crystalline minerals without the addition or removal of any material. In most cases, it occurs upon cooling below the temperature of mutual solubility. 

Read more: Sri Lanka - A Gem of an Island

How does the exsolution process of rutile occur in star corundum?

At temperatures of 1200-1400°C, titanium moves through the resulting expanded crystal lattice and between the oxygen atoms, exsolving into rutile needles. Other frequently encountered oriented oxide inclusions are hematite (Fe₂O₃) and ilmenite (FeTiO₃).

What is asterism?

Asterism is the star effect seen by reflection and scattering of light in cabochon-cut stones with suitably oriented rod-like inclusions or platelets. In corundum, due to the three-fold rotational symmetry of the basal pinacoid, networks of exsoluted syngenetic inclusions are oriented in three different crystallographic directions that intersect at 120°. The star image results from the incoherent superposition of reflected Frauhofer diffraction patterns, which arise when light is scattered around the network of inclusions. The cabochon in facts as a biconvex lens, which focuses the star image above the gem.  

What causes the asterism in 12-rayed black-star sapphires from Thailand?

Black star sapphires from Thailand contain inclusion networks of both the hematite-ilmenite series and rutile. The Fe-Ti epigenetic inclusions crystallise due to the presence of impurities of Fe and Ti in the host crystal as it cools after its formation, forming microscopic needles and platelets. The additional network of rutile needles parallel to the second hexagonal prism of the corundum host produces the second six-rayed star at 30° with respect to the first one. The observer will see a white six-rayed star perpendicularly superimposed over a yellow/golden six-rayed star.  

This study is about a large 112.64 ct ‘Ceylon Stars’ black sapphire of probable Sri Lankan origin that exhibits 12-rayed asterism. Raman spectroscopy combined with optical microscopy has been used to analyse both networks of needle inclusions in this sapphire as well as in smaller samples from the same source and in a black star sapphire from Thailand for comparison. 

Read more: Reconstructed Amber Broken Down

Raman spectroscopy surprisingly identified both networks of acicular inclusions in the giant 12-rayed black star sapphire as ilmenite. Typical Raman spectra for the ilmenite inclusions were characterized by a strong band at 678 cm⁻¹. The other vibration modes for ilmenite were 162, 194, 221, 256, 291, 329, 374, 451 and 597 cm⁻¹. The obtained spectra are in good agreement with natural ilmenite. The acicular inclusions parallel to the first-order hexagonal prism in each of the smaller 12-rayed star sapphires from Sri Lanka were identified as ilmenite by Raman spectroscopy. Ilmenite also constituted the second set except for one sample in which the second network consisted exclusively of rutile needles. Raman spectroscopy confirmed the presence of an Fe/Ti-rich oxide as well as rutile in the 12-rayed black star sapphire from Thailand.  

Optical microscopy of the 12-rayed black star sapphire at high magnification near the surface of the cabochon revealed some details about the microstructure of the growth bands. Networks of oriented needles and platelets - in three different orientations intersecting at 60°/120° were present within the basal plane. Compared to the growth bands, most of the acicular inclusions were oriented perpendicular and oblique at 30, or parallel and oblique at 60°. The density and the width of inclusions varied in different areas of the stone. Also, the average width of the inclusions oriented perpendicular to the growth bands of the host corundum was narrower than the inclusions oriented parallel to the growth bands. This explains the difference in sharpness between the two six-rayed stars. The needles responsible for the two stars were similar in colour, resulting into 12 brownish rays. Some larger plate-like shaped black inclusions reminiscent of magnetite with edges parallel or perpendicular to the acicular inclusions were observed. Strong transmitted illumination revealed a mainly dark blue body colour with some areas showing a more violet hue.    

The presence of a single mineral - ilmenite - as the cause of 12-rayed asterism in sapphire was documented here for the first time in the largest such gem known to the authors, a 112.64 ct black star sapphire of probable Sri Lankan origin. The sharpness of the rays correlates to the width of the inclusions, regardless of the identity of the mineral that causes them. The fact that it contains only ilmenite inclusions is consistent with its Sri Lankan origin, which is distinctive from the inclusion assemblage found in Thai stones. ■ 

This is a summary of an article that originally appeared in The Journal of Gemmology titled 'Large 12-Rayed Black Star Sapphire from Sri Lanka with Asterism Caused by Ilmenite Inclusions’ by Thanh Nhan Bui, Pascal Entremont and Jean-Pierre Gauthier 2017/Volume 35/ No. 5 pp. 430-435 

Interested in finding out more about gemmology? Sign-up to one of Gem-A's courses or workshops.

If you would like to subscribe to Gems&Jewellery and The Journal of Gemmology please visit Membership.

Cover image the 112.64 ct 'Ceylon Stars' sapphire, from the collection of P. Entremont, displays 12-rayed asterism, as shown here with pinpoint illumination positioned (a) over its centre and (b) obliquely. Images courtesy of P. Entremont. 

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The Fascinating History of Antique Turquoise Jewellery

In his third Gemstone Conversations column for Gems&Jewellery, Jewellery Historian and Valuer John Benjamin FGA DGA FIRV explores the fascinating history of turquoise and its use in jewellery design from the Shahs of Persia to the Art Deco design movement.

Read more

---

Birthstone Guide: Garnet For Those Born In January

If you're lucky enough to be born in January, vibrant garnet is your birthstone. A rainbow jewel of the gem world, garnet displays the greatest variety of colour of any mineral and is very often untreated, making it a rarity in the gem world. 

Read more

---

Getting Started with Quartz Inclusions

Do you know your calcite inclusions from your dumortierite, epidote, fluorite and rutile? Here, Charles Bexfield FGA DGA EG explores some incredible quartz inclusions and explains what to look for when shopping for quartz specimens.

Read more

---

Understanding Iridescence: Opals, Pearls, Moonstones and Fractured Stones

Iridescence has to be one of the most mesmerising and magical optical effects seen in gemstones. But have you ever wondered how it occurs? Gem-A's Collection Curator Barbara Kolator FGA DGA shines a light on this fascinating optical effect and tells us about the gems that are most likely to display it.

Read more

---

Hidden Treasures: Highlights of Gem-A's Gemstones and Minerals Collection

Gem-A Gemmology Tutor Pat Daly FGA DGA offers us a glimpse at some of the more unusual items in Gem-A's Gemstones and Minerals Collection.

Read more

---

Tanzanite: The Contemporary December Birthstone

Are you looking for the perfect festive gift for a December baby? Gem-A tutor Lily Faber FGA DGA EG considers tanzanite – one of three birthstones for December – and shares how this relatively new gemstone compares to its purple and blue-hued rivals.

Read more

---

Birthstone Guide: Turquoise For Those Born In December

Beautiful blue turquoise is one of three birthstones for the month of December (in addition to zircon and tanzanite). It is enriched with real cultural significance that can be traced back thousands of years. Here, we explore the blue shades of turquoise and explain what makes this gemstone so special...

Read more

---

Understanding the Cat's Eye Effect in Gemstones

Chatoyancy is the gemmological name given to the curious optical effect in which a band of light is reflected in cabochon-cut gemstones, creating an appearance similar to light bouncing off a cat's eye. Gem-A's Collection Curator, Barbara Kolator FGA DGA explains chatoyancy and highlights some of the many gems in which it can occur.

Read more

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Jade and its Importance in China

Jade has long been revered by gem lovers internationally, but nowhere more so than in China. But what is it that makes this gemstone so special? Gem-A's Assistant Gemmology Tutor Dr Juliette Hibou FGA gives us an overview of jade, how to identify it and its significance in Chinese culture.

Read more

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Highlights of Gem-A Conference 2019

The Gem-A Conference is always the highlight of our gemmological calendar! If you didn’t manage to make it, we’ve put together a few of the highlights from this year’s event to fill you in on what you missed, and whet your appetite for Gem-A Conference 2020!

Read more

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Deborah Craig FGA DGA, head of the Africa Team at International Women in Mining (IWIM) and board member within the organisation, reports on her recent trip to Malawi.

Peaceful, democratic Malawi remains one of Africa’s least-developed countries. Yet this small landlocked place, affectionately known as ‘The Warm Heart of Africa’, sits within the Mozambique Belt, surrounded by its famous gemstone-producing neighbours: Tanzania, Zambia and Mozambique. 

Read more: Ruby and Pink Sapphire from Aappaluttoq, Greenland

What is Malawi’s potential to join their ranks as a source of some of the world’s most beautiful coloured gemstones? Can Malawi’s nascent gemstone industry create prosperity for the country? In autumn 2016, Andrea Antonucci FGA and I travelled to Malawi to visit the Chimwadzulu Hill sapphire and ruby mine and meet with members of the local gemstone community. We began in Blantyre with John Chikokoto, the president of the Gemstone Association of Malawi (GAM). GAM was re-energised in 2015 with funding from the World Bank’s ‘Mining Governance and Growth Support Project’. 

Mr Chikokoto brought ruby and tourmaline crystals to show us. GAM members are mining sapphire, ruby, aquamarine, rhodolite, zircon and blue agate.

There is even a rumour that kimberlite has been discovered near the Mozambique border, but much of what we hear is merely speculation. The bulk of rough material is immediately exported out of Malawi, often illegally. Unlike Tanzania, Zambia and Mozambique, Malawi does not have a value-addition strategy, which would ensure more gemstones were processed in-country. He tells us if the gemstone industry is to grow, develop and provide long lasting economic benefits, his members need skills training at all stages of the value chain - mining, valuation, lapidary and marketing. 

These sentiments are echoed by Hellen Chasowa, regional chairperson south for Malawi’s Women in Mining Association (MAWIMA). GAM has around 2,000 members, of whom approximately 800 are women and also members of MAWIMA. Attracted to gemstone mining and dealing as an alternative to subsistence agriculture, which occupies most Malawians, MAWIMA’s members would also like to add value to the stones they are mining to increase their incomes and develop sustainable livelihoods. They are seeking project sponsorship for a tumbling machine and a drill, to make beads and create jewellery for Malawi’s burgeoning tourist trade. 

Read more: Discovering Unique Cameos of the Rainforest

Two companies, Nyala Mines Ltd and Columbia Gem House are working hand-in-hand to bring Malawi’s gemstones to the attention of the world market. Nyala Mines Ltd mines sapphire and ruby at Chimwadzulu Hill, and has created a fully-integrated, transparent supply chain extending from mine to retailer with its cutting, marketing and sales partner, Columbia Gem House. 

They would like the Nyala brand to equal quality, trust (disclosure of treatments) and social responsibility. The last is of critical importance when engaging with the economically disadvantaged communities close to the mine. Nyala works together with community leaders to understand how best to provide local support. To date, Nyala has built new school blocks, constructed boreholes for wells and upgraded the local health clinic. 

Chimwadzulu Hill is an eluvial corundum deposit discovered in 1958 about 145 miles south of Lilongwe, Malawi’s capital. The heavy minerals have been eroded by in-situ weathering and scattered down the sides of the hill, like sprinkles on top of an ice cream cone.

The presence of both chromium and iron mean that corundum is found here in a rainbow of colours: pale green, blue and yellow sapphires, but rubies and padparadscha sapphires are also found here. 

Over the years, the government, as well as various investors, have mined the deposit with varying degrees of success. In 2008, Nyala Mines Ltd acquired Chimwadzulu Hill, but the financial crisis, combined with rampant theft and high operating costs forced the mine to close. In 2013, Malawian national Abdul Mahomed acquired 80% of Nyala Mines Ltd bringing new life to the mine. Columbia Gem House, which had partnered with previous owners, reaffirmed their commitment to cut and market the stones. 

Chimwadzulu Hill is primarily a low-grade (in terms of carats per tonne) sapphire deposit; the rubies and padparadschas are a welcome bonus. The key to ensuring the mine’s profitability is to increase the volume of ore excavated and processed, thereby bringing down the mine’s operating cost per tonne. 

The current plant processes 30 tonnes of ore per day. Mr Mahomed would like to increase production significantly to 1,000 tonnes of ore per day. The new plant and equipment has been ordered and an environmental impact assessment has been filed, pending government approval. An increase in production will also hasten the removal of the overlying secondary deposits, hopefully exposing the primary source of corundum that Mr Mahomed believes lies below. 

Read more: Gem Central Exploring Ruby Treatments with Julia Griffith FGA DGA EG

It is time for Malawian gemstones to take their rightful place among the most beautiful gemstones in the world, while providing economic opportunity to Malawians. For this to happen, it is critical that the Malawian government implements value-addition strategies that ensure more rough material stays in-country to be cut and fashioned. There will be challenges, but small steps in skills training and market development can be taken at the local level, through associations such as GAM and MAWIMA, supported by Malawian and international partners. Nyala and Columbia Gem House have shown that operating in an ethical manner creates important benefits for local communities, as well as making good business sense. 

Deborah Craig would like to acknowledge the financial contribution of the Swedish Gemmological Society who helped make the trip possible. ■ 

Gem-A members can log in to read the full article Gems&Jewellery Spring 2017 / Volume 26 / No. 1

Interested in finding out more about gemmology? Sign-up to one of Gem-A's courses or workshops.

If you would like to subscribe to Gems&Jewellery and The Journal of Gemmology please visit Membership.

Cover image L-R John Chikokoto, Deborah Craig, Hellen Chasowa, Andrea Antonucci. Photo credit Deborah Craig. 

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The Fascinating History of Antique Turquoise Jewellery

In his third Gemstone Conversations column for Gems&Jewellery, Jewellery Historian and Valuer John Benjamin FGA DGA FIRV explores the fascinating history of turquoise and its use in jewellery design from the Shahs of Persia to the Art Deco design movement.

Read more

---

Birthstone Guide: Garnet For Those Born In January

If you're lucky enough to be born in January, vibrant garnet is your birthstone. A rainbow jewel of the gem world, garnet displays the greatest variety of colour of any mineral and is very often untreated, making it a rarity in the gem world. 

Read more

---

Getting Started with Quartz Inclusions

Do you know your calcite inclusions from your dumortierite, epidote, fluorite and rutile? Here, Charles Bexfield FGA DGA EG explores some incredible quartz inclusions and explains what to look for when shopping for quartz specimens.

Read more

---

Understanding Iridescence: Opals, Pearls, Moonstones and Fractured Stones

Iridescence has to be one of the most mesmerising and magical optical effects seen in gemstones. But have you ever wondered how it occurs? Gem-A's Collection Curator Barbara Kolator FGA DGA shines a light on this fascinating optical effect and tells us about the gems that are most likely to display it.

Read more

---

Hidden Treasures: Highlights of Gem-A's Gemstones and Minerals Collection

Gem-A Gemmology Tutor Pat Daly FGA DGA offers us a glimpse at some of the more unusual items in Gem-A's Gemstones and Minerals Collection.

Read more

---

Tanzanite: The Contemporary December Birthstone

Are you looking for the perfect festive gift for a December baby? Gem-A tutor Lily Faber FGA DGA EG considers tanzanite – one of three birthstones for December – and shares how this relatively new gemstone compares to its purple and blue-hued rivals.

Read more

---

Birthstone Guide: Turquoise For Those Born In December

Beautiful blue turquoise is one of three birthstones for the month of December (in addition to zircon and tanzanite). It is enriched with real cultural significance that can be traced back thousands of years. Here, we explore the blue shades of turquoise and explain what makes this gemstone so special...

Read more

---

Understanding the Cat's Eye Effect in Gemstones

Chatoyancy is the gemmological name given to the curious optical effect in which a band of light is reflected in cabochon-cut gemstones, creating an appearance similar to light bouncing off a cat's eye. Gem-A's Collection Curator, Barbara Kolator FGA DGA explains chatoyancy and highlights some of the many gems in which it can occur.

Read more

---

Jade and its Importance in China

Jade has long been revered by gem lovers internationally, but nowhere more so than in China. But what is it that makes this gemstone so special? Gem-A's Assistant Gemmology Tutor Dr Juliette Hibou FGA gives us an overview of jade, how to identify it and its significance in Chinese culture.

Read more

---

Highlights of Gem-A Conference 2019

The Gem-A Conference is always the highlight of our gemmological calendar! If you didn’t manage to make it, we’ve put together a few of the highlights from this year’s event to fill you in on what you missed, and whet your appetite for Gem-A Conference 2020!

Read more

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Rosamond Clayton FGA DGA FIRV MAE, a gemstone specialist and jewellery valuer, is often called upon as an expert witness in trials to identify and value precious stones. 

When did you get started in gemmology?

I had been working in Hong Kong on a contract posting when I married in the 1970s and I needed to find a new and interesting career. Fortunately, my search for a fulfilling subject to study coincided with the arrival of Marcia Lanyon FGA in Hong Kong, whom I met at a friend’s house one evening. 

I was soon enrolled on a foundation gemmology course and quickly became a fanatic. Many in our trade will recognise this ‘disease’. When I visited China in 1973 for a business trip with my husband, we were each only allowed 15 pounds of luggage, including handbag and camera; Webster’s Gems formed part of this allowance! 

I took my foundation exams in Hong Kong in 1974 and passed, but it was diamonds that interested me and therefore I needed to study for the Diamond Diploma. I was helped by Noel Deeks FGA DGA who taught the practical diamond grading at Sir John Cass College in London, but there was nowhere to study in Hong Kong, so I partly commuted to London (subject to load on British Airways). Noel Deeks introduced me to a Mr Shun Wai Woo FGA DGA, the only DGA in Hong Kong at the time, who worked in a senior capacity with his cousin, who had started the only diamond manufacturing company there. 

In addition, through a friend, I was introduced to Bill and Joan Hsu who had studied the residential GIA diamond course in Santa Monica and returned to Hong Kong to run a diamond wholesale business. I went to their office at least once a week and graded all their stock; they taught me how to survive in business in Hong Kong. 

How did you transition to the world of valuations?

When Marcia Lanyon left Hong Kong she passed her consultancy work with the Hong Kong tourist association on to me, so by this time I knew most of the retailers. My boss at the time, a shrewd Chinese business woman, saw an opportunity to open up new accounts with these retailers. After three years I moved to a retailer in Kowloon on the mainland, called Tse Lee Yuen. 

One Monday I was instructed by my employer that I would become the valuer! I was to value all the customers’ diamonds and jadeite. My protests fell on ‘dead ears’ as I was told my English was better than my Chinese colleagues’ and the valuations had to be written in English – there were no typewriters with Chinese characters – therefore there was no argument. 

How did your own business evolve?

In 1985 I set up my own valuation business in Hong Kong, which I sold when I returned to the UK in 1987. Initially, on return to the UK, I rented space with jewellery designer John Donald at 120 Cheapside who I knew through Marcia Lanyon. It was a matter of going back to the start on the Monopoly board, only saved by the fact that the NAG and Gem-A were housed together in Carey Lane (in close proximity to Cheapside), and I was soon taken under the wing of Philip Stocker FGA the NAG in-house valuer. He introduced me to the Academy of Experts, who provide training for those taking instruction as expert witnesses. 

Have there been any memorable moments that really stand out?

I have always enjoyed travelling abroad for work and my most memorable business trip was for a Chinese friend, who was chairman of a marine diamond mining company in Namaqualand, looking at the possibility of cutting diamonds mined there in Hong Kong or New York, where he lived. 

My cousin was working as a commercial pilot in South West Africa (now Namibia), so I flew to Windhoek with a commercial airline and she flew me from Windhoek to the mine in a Beechcraft Bonanza. We stayed the night at Okiep near Springbok, about 500 miles from Windhoek and the next day to De Punt, North of the Oliphants River. 

In earlier times this river was much larger and brought the diamonds down, it is thought from Lesotho, exiting into the Atlantic and carrying the diamonds north with the current, in the same process as the Orange River at a later stage. Due to the rough sea conditions, the members of the mining franchises were only able to dive on average four times a year and I was fortunate to be there on one of these occasions. Apart from a substantial yield of fine quality diamonds they brought up crayfish for our evening barbecues. 

Can you tell us a little bit more about your profession and what makes it unique? 

I had been instructed as an expert in jewellery cases in Hong Kong and this work in the field of gemstones and jewellery had always held the greatest interest for me. Importantly, it is necessary to train to supply reports as an expert witness in court proceedings and it is now becoming a requirement by the courts, not merely a wise precaution. The cases are varied but the civil cases frequently involve post loss assessment, divorce or some aspect of alleged unethical trading. 

A case set down for a High Court hearing can last a number of years from the preliminary report to additional reports in light of new evidence, experts meetings and finally the hearing which can frequently last a week or a number of weeks. A great deal of research is required, sometimes many months just for one item. No other type of valuation work provides this opportunity. 

What would your advice be for anyone who wants to get into what you do? 

For aspiring valuers today it takes time to obtain the required qualifications and experience and the process may seem costly. However, it would be hard to find another field of interest with so many enthusiastic and generous people willing to give their time and knowledge. As a valuer, even once the initial qualifications are obtained, without the wealth of knowledge available and help from those in specialist fields, it would not be possible to operate. In addition there is not a moment to lose in grasping every opportunity for further knowledge and training in every aspect of our rich world. 

My own career in the field of gemstones and jewellery has been a long and challenging path and, at the outset, I had not entertained the idea of being a valuer but I believe that there has been a revolution in the methodology of jewellery valuing in the UK and I am proud to be a part of it.

Top Tips: Becoming a Valuer

Essential qualifications:

Gemmology, diamond grading, Certificate of Appraisal Theory (CAT - the NAJ’s self-learning programme on valuation methodology). Join the National Association of Jewellers Institute of Registered Valuers (NAJ IRV). 

Concurrently with obtaining qualifications:

Try to obtain experience with a diamond wholesaler, coloured stone wholesaler or manufacturer. 

Network:

It is impossible to operate even as an experienced valuer without contacts. Visit auction houses, museums, attend lectures and most importantly attend The NAJ Loughborough Conference where workshops and lectures are provided on every imaginable valuation topic. ■  

Gem-A members can log in to read the full article Gems&Jewellery Spring 2017 / Volume 26 / No. 1

Interested in finding out more about gemmology? Sign-up to one of Gem-A's courses or workshops.

If you would like to subscribe to Gems&Jewellery and The Journal of Gemmology please visit Membership.

Cover image Rosamond Clayton and her colleagues from the Institute of Registered Valuers. All images courtesy of Rosamond Clayton. 

---

The Fascinating History of Antique Turquoise Jewellery

In his third Gemstone Conversations column for Gems&Jewellery, Jewellery Historian and Valuer John Benjamin FGA DGA FIRV explores the fascinating history of turquoise and its use in jewellery design from the Shahs of Persia to the Art Deco design movement.

Read more

---

Birthstone Guide: Garnet For Those Born In January

If you're lucky enough to be born in January, vibrant garnet is your birthstone. A rainbow jewel of the gem world, garnet displays the greatest variety of colour of any mineral and is very often untreated, making it a rarity in the gem world. 

Read more

---

Getting Started with Quartz Inclusions

Do you know your calcite inclusions from your dumortierite, epidote, fluorite and rutile? Here, Charles Bexfield FGA DGA EG explores some incredible quartz inclusions and explains what to look for when shopping for quartz specimens.

Read more

---

Understanding Iridescence: Opals, Pearls, Moonstones and Fractured Stones

Iridescence has to be one of the most mesmerising and magical optical effects seen in gemstones. But have you ever wondered how it occurs? Gem-A's Collection Curator Barbara Kolator FGA DGA shines a light on this fascinating optical effect and tells us about the gems that are most likely to display it.

Read more

---

Hidden Treasures: Highlights of Gem-A's Gemstones and Minerals Collection

Gem-A Gemmology Tutor Pat Daly FGA DGA offers us a glimpse at some of the more unusual items in Gem-A's Gemstones and Minerals Collection.

Read more

---

Tanzanite: The Contemporary December Birthstone

Are you looking for the perfect festive gift for a December baby? Gem-A tutor Lily Faber FGA DGA EG considers tanzanite – one of three birthstones for December – and shares how this relatively new gemstone compares to its purple and blue-hued rivals.

Read more

---

Birthstone Guide: Turquoise For Those Born In December

Beautiful blue turquoise is one of three birthstones for the month of December (in addition to zircon and tanzanite). It is enriched with real cultural significance that can be traced back thousands of years. Here, we explore the blue shades of turquoise and explain what makes this gemstone so special...

Read more

---

Understanding the Cat's Eye Effect in Gemstones

Chatoyancy is the gemmological name given to the curious optical effect in which a band of light is reflected in cabochon-cut gemstones, creating an appearance similar to light bouncing off a cat's eye. Gem-A's Collection Curator, Barbara Kolator FGA DGA explains chatoyancy and highlights some of the many gems in which it can occur.

Read more

---

Jade and its Importance in China

Jade has long been revered by gem lovers internationally, but nowhere more so than in China. But what is it that makes this gemstone so special? Gem-A's Assistant Gemmology Tutor Dr Juliette Hibou FGA gives us an overview of jade, how to identify it and its significance in Chinese culture.

Read more

---

Highlights of Gem-A Conference 2019

The Gem-A Conference is always the highlight of our gemmological calendar! If you didn’t manage to make it, we’ve put together a few of the highlights from this year’s event to fill you in on what you missed, and whet your appetite for Gem-A Conference 2020!

Read more

---

Although once known as 'bad luck', opals are fast becoming one of the most sought after gemstones in jewellery collections. But what makes one opal worth thousands and others mere pounds and pence?

Here, Gem-A Instruments manager, Samatha Lloyd FGA EG, offers a quick but essential guide to opal value factors and what distinguishes a fantastic specimen from an average one. 

COLOURS IN OPAL

Opal is composed of uniform spheres of silica, which form a grid-like structure. The spaces between these spheres contain a silica solution. When light passes through the spheres and hits the silica solution, it is diffracted, producing differing rainbow hues.

Read more: The Different Types of Opal

Colour play depends on the size of the spheres, for example, smaller spheres result in blue colours, but orange and red will be present when they are larger. The more uniform the grid-like structure, the more intense the colours will appear.

TYPES OF OPAL 

Customers may be most familiar with light opal, which makes up the majority of mined opal. It has base colours that range from white, to milky white and light grey, with varying degrees of colour play dancing on top.

If the body of the opal is transparent – also known as light crystal opal - the colour patches can be seen below the surface. It is these specimens that command exceptionally high prices. Your customers may also be familiar with black, or dark, opal, which has a dark body colour - sometimes enhancing the brilliance of the colours. This is the rarest and most valuable opal variety. 

OPAL VALUE FACTORS 

There are a number of factors that alter the value of opals. As mentioned, black opal can command higher price points than light opal (especially with an inky black body tone), although this is not to say that a fantastic light opal cannot be more expensive than a mediocre black opal. 

The brightness and brilliance of an opal is particularly important for its value, even if it is average in other areas. Therefore, lots of colours flashing on a dull stone may not command the same value as a gem with a higher degree of brilliance. 

We have already hinted at transparency, but this is also an important value factor. Light opal is much more desirable if it is transparent, with crystal opals with vibrant colours being particularly prized. 

A secondary and more complex layer of value arises when considering colours. The ‘dominant colour’ in an opal can affect its value, with red commanding the highest cost, followed by orange, yellow, green, blue, indigo and violet. However, do not forget, a blue-green brilliant stone will be more valuable than a dull red. 

OPAL PATTERNS 

In some rare cases, the diffraction of light within an opal can cause interesting patterns to arise. These patterns can increase the value of a stone. ‘Pinfire’ and small dot-like patterns are less desirable than bold ones, such as stripes, peacock feather shapes and broad brushstroke-like flashes of colour. 

ETHIOPIAN OPAL VS AUSTRALIAN OPAL

Customers may ask why one opal costs thousands of pounds, while another is mere hundreds or less. The answer could lie in its origin. Australia is a phenomenal source of opals and produces some of the world’s most incredible specimens.

Crucially, opals from this region have a lower water content, which means they are less susceptible to drying-out and less likely to exhibit ‘crazing’ - hairline fractures that impact the durability of the stone.

In contrast, Ethiopia is a newer source of opals, but some material has been found to have a much higher water content, making it unreliable and potentially unsuitable for jewellery. 

With thanks to Hatton Garden-based gemstone supplier, Marcus McCallum FGA, for taking these striking photos of Ethiopian and Australian opals.

Read more facts in The Opal Story by Andrew and Damien Cody, available in the Gem-A library. ■  

Gem-A members can log in to read the full article Gems&Jewellery Spring 2017 / Volume 26 / No. 1

Interested in finding out more about gemmology? Sign-up to one of Gem-A's Short Courses or Workshops.

Cover image example of Australian opal. All images courtesy of Marcus McCallum.