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. 

Garnet is recognised for its rich history as a favourite gemstone of Victorian royalty, Ancient Egyptian pharaohs and the Roman elite. Its painter’s palette of shades, varieties and hues makes it a popular choice for jewellery creations.

Garnet Colours

Garnet is commonly seen in a striking spectrum of red, from orange rust and deep-violet to rich royal reds reminiscent of a pomegranate fruit.

The term 'garnet' comes from the name ‘gernet’, a 14th century Middle English word meaning dark red, further deriving from the Latin 'granatum' meaning 'pomegranate'. This connection was probably made due to the resemblance of garnet crystals to the seeds of a pomegranate.

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Demantoid garnet with clear horsetail inclusions. Image by Pat Daly.

Today, garnet is the term for a group of minerals found in various colours from the red pyrope garnet to the zesty green tsavorite garnet.

Read more: 5 Things to Consider Before Starting the Gem-A Gemmology Foundation

The range of garnet colours comes from trace metals such as manganese, iron or chromium. Variations in chemical composition between different species of garnet result in a range of hardness on the Mohs scale from 6.5-7.5.

Garnet Varieties

There are five main species of garnet that have the same crystal structure but slight differences in their chemical composition.

• Almandine Garnet: purple to orangey reds
• Pyrope Garnet: purples to orangey reds
• Spessartine Garnet: oranges to yellows
• Andradite Garnet: yellows to yellowish greens
• Grossularite Garnet: colourless to yellow, to orangey red, to vibrant green (rare)

Polariscope garnet peridotite. Image by Pat Daly.

Where Do Garnets Come From?

Garnets are commonly found in many countries worldwide, including Australia, India, Czech Republic, Myanmar, Brazil and Sri Lanka to name a few.

In the 19th century, garnet adorned many decorative creations of the famous jeweller Peter Carl Fabergé and was a gem highly favoured by the Russian royal family. Bohemia and Russia were documented as primary locations to source garnet throughout the 19th century. Today, Tanzania and Namibia are prized for their abundance of garnets.

Left: Spessartine garnet with feather inclusions. Right: Hessonite garnet with crystal inclusions. Images by Pat Daly.

Garnet Folklore and History

Garnet has an extensive history and rich ancient folklore that spreads across many eras. Legend has it that garnet - known as the ‘Gem of faith’ - has powers of good health, prosperity and peace.

Read more: Gem-A Confirm Oldest Known Carved Tourmaline

The bright and striking nature of garnet is thought to be fitting to the vibrant personalities of those born in the month of January. It is thought that individuals who wear this stone can enter the New Year with a sense of renewed purpose, hope and lasting happiness.

Garnet Meaning

This gemstone was once used as a talisman of victory and protection by those going into battle. Many warriors would wear the stone to ward off disease and would place it on their battle wounds as a catalyst for healing.

Read more: Hidden Treasures of the Gem-A Gemstones & Mineral Collection

Historical reference to garnet date back even further to the time of the Ancient Egyptians, who utilised the stone as inlays in their jewellery and decorative carvings. Garnet was also a popular choice for signet rings worn by the Ancient Romans, especially when carved into intaglios to seal important documents. Hailed for its health benefits, garnet was a prized possession for clergymen and nobility across many centuries.

Famous Garnet Jewellery

Today, garnet is used in a wide range of jewellery collections and bespoke pieces such as rings, statement pendants as well as tiaras. Its array of colours and transparency make for spectacular pieces of considerable value.

Read more: The History of Garnet in Antique Jewellery

One of the most famous examples of garnet jewellery to date is a pyrope garnet hair comb from the Victorian era, housed at the Smithsonian National Museum of Natural History. The pyrope garnets that embellish the tiara-shaped comb originated from the Bohemian Mines (now part of the Czech Republic). Rose-cut garnets were often mounted in gold plate or yellow gold - a popular style during the Victorian era.

Whether you are looking for a talisman of prosperity for 2020 or a gift for someone born in January, the fire and sparkle of garnets are timelessly beautiful.

A Malayan garnet with rutile needle inclusions. Image by Pat Daly.

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What is Associate Membership of Gem-A? Find out here.

Our Short Courses and Workshops at the perfect way to enhance your gemmology knowledge in a short space of time. Find out more here.

Cover image: Almandine garnet with crystal inclusions. Image by Pat Daly © Gem-A.

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Glass Simulants of Gems and Enhancement of Natural Gem Materials in the 16th Century

Guy Lalous ACAM EG, summarises the state of making glass simulants of gems in the 16th Century, as well as exploring the historical information we have available on the enhancement of natural gem materials.

What about gem treatments?

Many gemstones can be treated to alter their colour and clarity. Today, gemmologists are confronted to a broad spectrum of treatments ranging from the simple to the highly sophisticated as well as the easily detected to the highly elusive. Treatments include: bleaching, coating, dying, fracture filling, heating, impregnation, high pressure, high temperature, irradiation, laser drilling and lattice diffusion.

What about the origins of gem treatments?

Heated carnelian was found in Tutankhamun's tomb-dating to at least 1300 B.C.C. Plinius Secundus (First Century A.D) is the earliest written source on gem treatments. Pliny discusses many gemstone-enhancement techniques including foils, oiling and dying that are still in use today, almost 2,000 years later. The "Stockholm Papyrus" made about 400 A.D. in Greek-speaking Egypt contains 73 recipes which deal with the falsification of pearls and gemstones; representing the oldest extended recipe collection dealing with gems. In 1502 "The Mirror of Stones" was published, a fascinating book by Camillus Leonardus, a physician and astrologer of Pesaro, Italy. It discusses gem treatments and simulants and also how to identify those stones that are "not true" and the importance of experience and knowledge in this subject.

In the 17th Century, we have the Gemmarum et Lapidum Historia of 1609 by Boetius de Boot, a physician of Bruges. In the French translation of 1644, there is discussion in Chapters 20 to 22 of the decolourising by heat of sapphire, topaz, amethyst and the like, to produce diamond imitations; the dyeing of stones, mostly with metal compounds, an extended discussion of metal foils and an obscure description on how to harden gemstones. By 1820, agate dyeing in Idar-Oberstein had been perfected to the point that it was practiced on a large scale and the agate sold as treated stone. For the first time, a gemstone material was altered commercially and marketed as such and not as a natural material. By the middle of the 19th Century, gemmology had turned into a science (K. Nassau).

What about man-made glass?

Man-made glass dates back to approximately 5000-4000 BC, this took the form of glazes used for coating stone beads. It was not until 1500 BC that the first hollow glass container was made by covering a sand core with a layer of molten glass. Glass blowing became the most common way to make glass containers from the First Century BC. As from the First Century AD colourless glass was produced and coloured by the addition of colouring agents. Glass has been used as a substitute for emerald and other fine gemstones since at least the days of ancient Rome. Skills for glass making spread throughout Europe and the Middle East when the Roman Empire disintegrated. It was not until the full development of the Renaissance, in the mid-1500s, that a writer purposely gave the tedious details of the entire process of glass 'gem' making. This author was Giovan Battista Della Porta.


Figure 1: These 'emerald' and 'amethyst' glass eardrops in the Renaissance style were presumably assembled in the second half of the 16th century. The mounting is partially silvered copper. The green glass 'gems' are 6 mm in diameter. Courtesy of a private collection near Rome, Italy; photo by Carlotta Cardana.

Giovan Battista Della Porta was the first to publish in print recipes for making glass simulants of gems, in addition to information on the enhancement of natural gem materials. His Magiae Naturalis (1558), originally written in Latin, enjoyed vernacular translations in several European languages. The second, vastly improved edition (Della Porta, 1589), again in Latin, did not enjoy the same popularity - possibly because the first one has saturated the market or, alternatively, because the Catholic Church has enforced rules that made alchemy a forbidden practice and even the title Magiae became suspect. In spite of such restrictions, both editions contributed to making glass 'gems' popular decorative objects and to increasing their trade. During Baroque times, interest in glass 'gem' making reached an acme, and Della Porta's treatise was even translated into English in 1658.

Figure 2: This portrait of Giovan Battista Della Porta at the age of 50 is from the title plate of the 1589 edition of his Magiae Naturalis.

His modus operandi was well known. For every secret he learned, he first checked for other possible sources by reading books by old masters, after which he tested the results by performing experiments in his home laboratory. Glassmaking was one process that could be performed with a kiln, a rather simple apparatus. The preparation of certain special glasses (e.g. coloured ones suitable for simulating gems) involved knowledge that had been an artisan secret until it was released by Della Porta in his original 1558 edition of Magiae Naturalis.

In Book III of Magiae Naturalis, 1558, Della Porta wrote three chapters related to glass that followed the descriptions of other chemical operations, such as sublimation, distillation, purification and melting, plus miscellaneous recipes on how to repair broken corals, pearls and gemstones. He did not care to deal with how to make ordinary glass, but he proceeded directly to release the technicalities on how to prepare the special colourless glass that would be suitable for making coloured glass, so as to imitate gem materials. In chapter 16 he summarised the preliminaries, recommending the use of very finely ground silica mixed with fluxes.

In chapter 17 he made a digression aimed at explaining how natural gem materials acquire their colours and shifted to recipes on enhancing colour by using various natural pigments, by slowly diffusing them from the surface to the bulk of the gem under the slow action of fire. Then he returned to recipes intended to add weight to glass without modifying its hardness. In particular, he recommended adding lead to the already prepared colourless glass only while it melts, so as to increase its brilliance and weight. After another digression, he ended Chapter 18 with a series of explanations on how to obtain attractive 'gem' glass by carefully mixing colourless glass with pigments while it melts. The resulting gem simulants would resemble diamond, emerald, sapphire, pyrope, topaz, olivine, chalcedony, etc. The final recommendation was that the crucible containing the molten mix should be kept under close supervision, as excess heating would make the colour fade away.

In 1589, Della Porta, by now a mature scientist, reworked his Magiae Naturalis, expanding it from four books to 20. The in-folio sized text dealing with gems grew from five ordinary pages to a complete Book VI encompassing 10 dense pages and distributed over 13 chapters. Actually, only Chapters 1 to 5 concern glass gem simulants and Chapters 7 to 13 mostly concern the enhancement of gem materials. Everything is described in much greater detail than in the previous edition. After an introduction, Della Portas begins Chapter 1 with a careful description for the preparation of reagents for glass gem making, beginning with two fluxes. Chapter 2 recalls that silica is the main constituent of any glass gem. The raw silica can be either crystal or flint, or even round pebbles; the best of are said to be those gathered from the river Thames.

Chapter 3 describes in detail the furnace and the instruments to be used and Chapter 4 teaches how to prepare pigments. Chapter 5 is the core of the entire process. Indeed, it is titles "How gems are coloured". The pigments are blended with the previously prepared colourless glass while it is molten, so that they mix homogeneously. The recipe for glass used to simulate emerald is given last because the preparation requires a long exposure to fire. The following chapters describe various enhancements of natural gem materials and then move onto enamels, coloured metal sheets for reflection, etc. The author ends book VI, Chapter 13, with the short but factual statement: "This is all what we experimented on gems so far".


Figure 3: The title page of Magiae Naturalis Libri XX, 1589 edition, shows the titles of all 20 books composing this volume.

The second half of the 17th Century in England was characterised by an economic revival with increasing interest for science in general, including those books penned by 'writers of secrets'. The practice of publishing 'secrets', although unwelcome to many, contributed to the development of both science and the economy. In particular, it is significant that Della Porta's Magiae Naturalis, intended for completely different purposes and contributing only poorly to the 'scientific revolution' because of its still rather alchemical bent, eventually helped speed up the English industrial revolution.

This is a summary of an article that originally appeared in The Journal of Gemmology entitled 'Counterfeiting Gems in the 16th Century: Giovan Battista Della Porta on Glass 'Gem' Making'' by Annibale Mottana 2017/Volume 35/ No. 7 pp. 652-666

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: Title page of the first english translation of Natural Magick in 1658, the title page of Magiae Naturalis Libri XX, 1589 edition and the frontispiece of the english translation of Natural Magick, 1658.


The Fascinating History of Antique Turquoise Jewellery

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

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

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

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

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

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

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

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 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

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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Birthstone Guide: Amethyst for Those Born in February

Gem-A gemmology tutor Lily Faber FGA EG explores the history of amethyst and its significance as the February birthstone.

Amethyst is a well-known, purple variety of quartz that is February’s birthstone. Fashioned pieces can vary from a lighter lavender to a deep, saturated purple.

In ancient Greece, it was believed that if worn or used as a drinking vessel, the wearer would be protected from becoming drunk, hence, its name is derived from the Greek words meaning “not drunken”.

Read more: What is the Meaning of Amethyst? 

It is also believed by some that the stone will bring you luck, serve as an antidote to poison, increase your intelligence and protect you from magic spells.


Amethyst quartz with ribbon-like inclusions. Image by Pat Daly.

Various localities include India, the USA, Australia and Brazil, which is one of the most important sources today. Historically, amethyst was mined in Siberia and Saxony (Germany).

Amethysts in History 

In keeping with February’s holiday of St. Valentine’s Day, it is said that St. Valentine wore a signet ring set with an amethyst intaglio carved with an image of Cupid.

Amethyst was also worn in the finger rings of bishops, and can be found in the Crown Jewels fashioned as a faceted orb sitting atop the Star of Africa diamond in the sovereign's sceptre.

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


Amethyst quartz with tiger stripe inclusions. Image by Pat Daly.

Historically, aristocratic and royal families the world over have prized the gem in different eras. One such monarch was Queen Alexandra, wife of King Edward VII, who owned a gorgeous amethyst tiara containing several high quality large, oval-shaped stones from the mines of Siberia.

Find Out More! Get Started with the Gem-A Gemmology Foundation Course

She also commissioned a necklace that could also be converted into a tiara. These pieces are sadly no longer in the Royal Collection as they were sold at auction in the 1940s.


Amethyst quartz jewellery set. Image by Pat Daly.

Amethyst Crystals, Inclusions and Colours

If sold as a rough specimen, amethysts are often seen as individual crystals with one broken end where it was detached from the host rock. More often, they are sold in the form of a geode cluster.

Geodes are cavities or pockets that are lined with many crystals of various sizes. Often, the colour is concentrated in the tips of the crystals, thus leading to a great variety in saturation of colour from pale to deep purple.

Read more: Gem Quality Amethyst From Rwanda

An inclusion that is typical, if not diagnostic of amethyst, is the tiger stripe. It is a healed fracture that can occur when the stone twins. Amethysts are either one consistent colour or have angular colour banding with alternating light and dark colour zones.

Amethyst Care and Caution

Amethyst is a relatively hard stone at 7 on the Mohs’ Scale of Hardness, but only just! It is softer than other stones like sapphires, and as such, can be susceptible to chips and fracture.

The colour of some stones can fade when exposed to sunlight, so take care if displaying in a vitrine or shop window. When cleaning, do not use an ultrasonic cleaner in case there are any small inclusions or internal fractures that may expand during cleaning. Use warm soapy water and a very soft brush to clear away dirt.

Read more Gem-A Birthstone Guides here

Do you want to know more about gemstones and the study of gemmology? Discover the Gem-A Workshops or speak to our Education team

Cover image: Amethyst crystal quartz with detachment marks. Image by Pat Daly, Gem-A.


The Fascinating History of Antique Turquoise Jewellery

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

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

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

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

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

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

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

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 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

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


Additional Info

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Gemstone of Passion: Padparadscha sapphire

Considered to be among the most beautiful of the corundum gems with its delicate colour, Padparadscha sapphire has recently hit the headlines thanks to Princess Eugenie of York’s engagement ring. Here, we explore this majestic gemstone fit for royalty.

Om mani padme hum – “Hail the jewel in the heart of the lotus”
- Buddhist Mantra

With recent royal exposure placing this gemstone in the media limelight, the public has been left with a burning question - what exactly is a Padparadscha sapphire?

Whilst considerably unknown to most, Padparadscha sapphires, recognisable for their delicate salmon pink tones, are prized among connoisseurs of the gem world. Just like other sapphires, the Padparadscha has a hardness of 9 on the Mohs scale, making it one of the hardest gemstones in the world (and ideal for engagement rings!). 

Sapphires get their colour from different trace elements. The presence of iron and titanium is responsible for blue tones, while traces of chromium cause pink tones. Ruby red is a result of more chromium present in the stone’s chemical composition. The Padparadscha sapphire is the rarest form of sapphire corundum, balancing on the colour boundary between pink and orange.

Deriving from the Sinhalese word for ‘aquatic lotus blossom’, the Padparadscha has stirred much debate amongst gemmologists, buyers and collectors about what colour spectrum constitutes a Padparadscha over, say, a pink sapphire or orange sapphire. Like all gemstones, Padparadscha sapphires are not easily identified as they have their own individual colour zoning with some displaying lighter mediums of pink and orange or colour zoned with yellow. In terms of value, this type of sapphire increases in value as the saturation of colour increases.

The rarity of these sapphires is due to their limited locale and sourcing. Whilst commonly found in Sri Lanka, Padparadscha sapphires are also found in Tanzania and Madagascar. Padpardaschas sourced from Madagascar are usually pinker than orange but now contribute to a wide percentage of the stones available on the market today, whilst those from Tanzania tend to be browner. Whilst many gemmologists insist that the only ‘real’ Padpardschas come from Sri Lanka, new sapphires from Madagascar continue to be a beautiful and unique addition to the market supply. 

Read more: An examination of the problem of separating pink sapphire and padparadscha from ruby

Today, many Padparadscha sapphires from Madagascar are heat-treated to enhance their pinkish colour at much lower temperatures to those sourced from Sri Lanka. A widespread treatment for corundum that induces the orangish-pink colour is Beryllium diffusion. The market is awash with these treated stones, therefore a lab report is essential when purchasing a naturally coloured Padparadscha sapphire.

Of course, Padparadscha sapphires have caught the attention of the media since Princess Eugenie of York, the granddaughter of Her Majesty the Queen and daughter of Prince Andrew, Duke of York, and Sarah Ferguson, Duchess of York, got engaged to wine merchant, Jack Brooksbank, in January 2018.

Her ring, which is not dissimilar to the ring Prince Andrew presented to Sarah Ferguson in 1986, features an oval-cut Padparadscha sapphire surrounded by a halo of diamonds. This is set on a yellow gold band with two further tapered diamonds at the shoulders.

Will Padparadscha sapphires be the surprise hit of 2018? Perhaps the Tucson and JCK trade events in January and June, respectively, will reveal a surge of popularity for this particularly lovely sapphire.

Gem-A would like to thank Richard Hughes of Lotus Gemology for his support in compiling this article. 

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: Princess Eugenie and Jack Broosbank via The Royal Family, Instagram. A 4.5ct unheated Padparadscha sapphire ring courtesy of the Somewhere In The Rainbow Collection


The Fascinating History of Antique Turquoise Jewellery

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

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

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

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

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

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

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

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 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

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


Additional Info

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An Endowed Chair in Gemology: First of its Kind in the World

The RealReal, the leading authenticated luxury consignment company, today announced a first-of-its-kind collaboration with the University of Arizona to create a new degree program for gemology. The RealReal is funding an endowed chair in the UA College of Science with the intent of helping the University of Arizona develop new research and technology. An undergraduate program will be offered, along with a graduate program for master's and PhD students emphasizing gemological research and skills will be made possible through this endowment. Finally, Gem-A (Gemological Association of Great Britain) is also partnering with the UA and The RealReal to allow students in the program to obtain their individual gemology certification.

As a key leader and innovator in the industry, The RealReal is joining the University of Arizona and Gem-A to further their shared values of education, innovation, and expertise. Together, they will develop unique technologies to enhance the study of gemology. For The RealReal, these advancements will also provide its gemologists, buyers, collectors, and potential sellers with elevated knowledge and information.

The new degree program will be located in Tucson, Arizona, the mineral and colored stone capital of the world. Students will learn on campus and in state-of-the-art labs located in the University of Arizona's new Gem and Mineral Museum in downtown Tucson.

"As the market leader in the jewelry resale market, we have always invested heavily in gemologists, research, and technology," said The RealReal CEO Julie Wainwright. "Collaborating with University of Arizona on this new degree program will enhance our efforts and the entire industry. We have had great success working with University of Arizona gemologists in the past and are extremely impressed with their expertise. We are excited to share their knowledge with the world."

"The RealReal is clearly an innovator in the luxury space. The University of Arizona is a known innovator in many aspects of retail, forensic sciences, and development of novel programs.  I am thrilled that these two entities who are currently leading in their respective fields are now working together to build this gemology program. These partnerships are how transformative changes happen." - Joaquin Ruiz, Dean, UA College of Science; UA Vice President for Innovation; Executive Dean of the Colleges of Letters, Arts and Sciences

About The RealReal

The RealReal is the leader in authenticated luxury consignment. With an expert behind every item, we ensure everything we sell is 100% real. We have 60+ in-house gemologists, horologists and brand authenticators who inspect thousands of items available online each day. As a sustainable company, we give new life to pieces by brands from Chanel to Cartier, and hundreds more, supporting the circular economy. We make consigning effortless with free in-home pickup, drop-off service and direct shipping. At our store in SoHo NYC customers can shop and consign and meet with our experts to learn more about luxury authenticity and sustainability. In eight Luxury Consignment Offices across the country, our expert staff provides free jewelry, watch and handbag valuations.

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Coloured Gemstones from Brazil: Past, Present and Future

Guy Lalous ACAM EG presents us a historical review, and an updated overview, of the Brazilian coloured stone industry. His latest Journal Digest from Gem-A’s Journal of Gemmology (Winter 2017. 35.8) also examines the effects of China’s emergence as a consumer market on Brazil’s gem industry.

Recent information on Brazilian gem occurrences is presented from data compiled by the Brazilian National Department of Mineral Production (DNPM) and other resources.

This suite of morganite (16.69–22.22 ct) was cut from Brazilian rough
Figure 1: This suite of morganite (16.69–22.22 ct) was cut from Brazilian rough. The gems were fashioned into various custom cuts, including (from upper left to lower right) Concave, Super Trillion, Deep Concave and StarBrite. Courtesy of John Dyer; composite photo by Ozzie Campos.

The history of Brazilian gemstones began with the early colonisation period. No gem deposits were found until 1573, when emeralds were discovered in the present-day Governador Valadares area. In the late 17th century, the legendary gold mines of Sabarabussu were discovered, located to the east of the present city of Belo Horizonte.

The ensuing rush then expanded north, unearthing the first diamond deposits a few decades later near the town that would become Diamantina. The exploration for gold and diamonds overshadowed other gem mining activities until the 19th century, apart from the Imperial topaz deposits found nearby in the old Minas Gerais capital of Ouro Preto. It was during this time that the term ‘garimpeiro’, which refers to independent miners, emerged.

Germans originating from Idar-Oberstein immigrated to the present-day state of Rio Grande do Sul, and to the north-eastern part of Minas Gerais, after Brazil’s independence from Portugal in 1822. During this period, Idar-Oberstein was experiencing economic troubles as the production from its agate mines dwindled.

The immigrants brought their cutting and polishing techniques with them, and initiated the first stage of development for the modern Brazilian coloured stone industry.

Among the most notable early finds was the 110.5 kg Papamel aquamarine, discovered in 1910 in the Marambaia Valley, as well as numerous emerald deposits. On the eve of World War II, gem-related activities in Brazil were mainly limited to mining, while the end of the war saw the widespread closure of industrial mineral mines in Minas Gerais. Many of these mines turned exclusively to gem production and, accordingly, local lapidary and other trade activities grew dramatically. The latter half of the 20th century was also marked by the emergence of a Brazilian jewellery industry.

What about Brazilian Emeralds?

Emerald is the green variety of the mineral beryl, coloured by chromium and vanadium.  These trace elements are normally concentrated in quite different parts of the Earth’s crust, but complicated geological processes enable these contrasting elements to find each other, and crystallise into one of the world’s most beautiful gemstones.

Geological Processes of Brazilian Emeralds

Brazilian emerald mineralization belongs to the classic biotite-schist deposit, which was formed by the reaction of pegmatitic veins within ultrabasic rocks. The granitic pegmatite injection makes the emerald crystallise at the contact zone between these chemically contrasted rocks.  The pegmatite brings beryllium, while the ultrabasic rock contains chromium and vanadium, and the reaction between them is called metasomatism.  This reaction is, however, only possible when geological fluids are present enough to ensure the transportation of the elements.  Pegmatite-free emerald deposits, linked to ductile shear zones, are also known in Brazil (G. Giuliani).

Weighing 6.11 cm, this emerald is unusually large for clean material from Brazil
Figure 2: Weighing 6.11 ct, this emerald is unusually large for clean material from Brazil. Courtesy of Paul Wild; photo by Jordan Wilkins.

Brazilian emerald production occurs in three states: Goiás, Bahia, Minas Gerais.  The first emerald site in modern times was discovered in 1912 in the deep south of Bahia State, near Brumado. Other emerald discoveries followed in the early 20th century at Ferros, in Minas Gerais; at Itaberaí, in  Goiás and at Anagé in Bahia.

More recent discoveries include: Itabira (1977) and Nova Era (1988) in Minas Gerais; at Santa Terez­inha de Goiás (1981) in Goiás; and in the Serra de Carnaíba region (1983) of Bahia.  Since the 2000s, Brazil has been ranked third among the world’s leading emerald producers, behind Colombia and Zambia.

Paraiba Tourmaline from Brazil

Paraíba tourmalines represented the first recorded instance of copper occurring as a colouring agent in this mineral. The blue-to green colours are primarily due to copper (Cu2+).


Figure 3: The bright coloration shown by Paraíba tourmaline (here, 5.73 ct) as well as its rarity have contributed to its high value. Photo and stone courtesy of Paul Wild.

Paraíba tourmaline—for its singularity and its profitability— became perhaps the most important discovery of the 20th century. Uncovered for the first time in 1987, in the São José da Batalha district of Paraíba, this tourmaline’s unique ‘neon’ blue-to-green coloration contributed to making it one of the most valuable coloured stones on the global market. Production of Paraíba tourmaline has, unfortunately, dwindled in recent years.

Global Gemstone Trade - The Role of Brazil 

In the late 1990s, Brazilian gems were mainly exported to the United States, Europe and Japan, with gem exports to Hong Kong and India increasing too. Finally, another major player emerged: China. The increase in exports of rough gem material to Asia has become very significant and, for a time, most of it was cut and polished in India and China.

Chinese brokers began to arrive in the quartz-producing areas at the beginning of the 2000s. These brokers bought most of the cheaper gems, contributing heavily to a rise in mining activities. Over the years, Chinese dealers acquired a greater variety of stones, showing a preference for tourmaline, especially rubellite.

One consequence of the increasing trade with China, though, has been the collapse of Brazil’s domestic gemstone cutting and polishing industry for low-value materials. The negative effect on local economies is particularly apparent in north-eastern Minas Gerais. In Teófilo Otoni, of the 2,700 lapidary businesses operating in 1993 only 360 remained in 2005. In 2011, China was the main partner in Brazil’s gem commerce, with 2013 seeing Brazil export 60% by weight, or 25% by value, of its output to China (up to 50% by value if Hong Kong is included).

Brazil, however, still remains significant for cutting higher-value gemstones. Teófilo Otoni and Governador Valadares remain the major gem cutting and trading centres. Various urban centres host the country’s main gem fairs, which are small venues compared with other international shows.

An important factor to note is the informal trading of gems; several hundred individuals travel around the country and acquire rough material to sell later in the metropolitan areas. The widespread adoption of modern technology, such as the internet and digital cameras, has revolutionised traditional methods of trading over the past decade, making middlemen somewhat obsolete.

Other factors have also diminished Brazilian gem production, such as the evolution of the international market. Many African countries now produce a larger variety and quantity of gems than they did a couple of decades ago, and those stones are usually sold at lower prices than those from Brazil. The high cost of mining is another reason for the recent decline in mining and production. According to the DNPM, there were 2,294 gem occurrences in 401 different municipalities as of 2013, with 49.3% of them in Minas Gerais and 19% in Rio Grande do Sul.

What about Santa Maria Aquamarine?

One of the rarest and most expensive varieties of aquamarine, the "Santa Maria", has a deeply saturated blue colour, with no hint of green or yellow. Named in honour of Santa Maria de Itabira where these stones were first discovered, the original deposit is now almost depleted, and today most of the Santa Maria colours are also found in several sub-Saharan countries of Africa, including Mozambique.

The colouring process is due to the Fe2+ - Fe3+ charge transfer. This feature is associated with intense absorption and strong pleochroism, and this process cannot be induced by heat treatment. The stones are nearly colourless in the direction of the optic axis, and intense dark blue perpendicular to the optic axis.

Figure 4: This 22.93 ct aquamarine is from Santa Maria in Minas Gerais. Courtesy of Paul Wild; photo by Jordan Wilkins.

Quartz and Topaz from Brazil 

Quartzes are abundant in Brazil. Stunning crystal clusters, appreciated by collectors, come from hydrothermal veins found in the Curvelo and Corinto areas of Minas Gerais. Rose quartz is found in pegmatites in the north-eastern part of Minas Gerais, while rutilated quartz has been produced mainly in the Novo Horizonte District of Bahia State.

Huge amethyst geodes, and most of the agates of the country, have been mined in abundance in Rio Grande do Sul. Citrine is mined there as well, but most of the citrine produced and exported from Brazil is actually heat-treated amethyst.

Figure 5: This large colour-zoned tourmaline from Brazil weighs 144.75 ct. Courtesy of Paul Wild; photo by Jordan Wilkins.

The country accounts for much of the world’s topaz production. Many stones are colourless, or tinged very light blue, and laboratory irradiation creates the bright blue colour. A post irradiation annealing is performed by a heat treatment of the topaz for several hours at around 200°C. The production of the rare and famous orange to orange-pink Imperial topaz has, however, greatly diminished, and good-quality material is particularly scarce on the local market.

Figure 6: The colour of this Swiss Blue topaz (13.73 ct, StarBrite cut) was produced by laboratory irradiation, using colourless or pale blue starting material from Brazil. Courtesy of John Dyer; photo by Ozzie Campos.

More Gemstones of Brazil 

Beryl production is dominated by light to medium-dark blue aquamarine, of which Brazil may be one of the largest exporters, with other beryls including heliodor and morganite. Most production of chrysoberyl is still located in Minas Gerais and Bahiam, but good quality Alexandrite is now harder to find locally and only small quantities are available. Collectively, Emeralds and other beryls, tourmaline, topaz and all types of quartz are the most widely mined coloured stone resources nationwide.

What's Next for the Brazilian Gemstone Industry?

Improved living conditions in rural areas have led to an evolution of the workforce, which is becoming less interested in, and less reliant upon, mining via illicit operations. Brazilian gem exports remain robust and gem mining is seeing a shift toward bigger and more professional companies.

The quantity of mining areas remains substantial and, probably, to a large extent underexplored. Yet, the future of the Brazilian gem industry may depend more on social issues, global market trends and an ability to establish efficient trade relationships.

This is a summary of an article that originally appeared in The Journal of Gemmology entitled '‘Coloured Stone Mining and Trade in Brazil: A Brief History and Current Status’ by Aurélien Reys 2017/Volume 35/ No. 8 pp. 708-726

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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Characterising Mexican Amber From the Yi Kwan Tsang Collection

Guy Lalous ACAM EG is on-hand to summarise some of the more in-depth articles from Gem-A's The Journal of Gemmology. Here, he delves into a feature on Mexican amber and the use of FTIR spectroscopy to determine provenance from the Winter 2017 issue. 

Amber is an organic gem. Organic gems are the products of living, or once-living, organisms and biological processes. Amber derives from fossilised resins produced by prehistoric trees.

Such resins are produced by plants in response to certain circumstances, such as defence against insect pests or protection of wounds.The most important resin-producing plant families are classified among the gymnosperms (conifers) and the angiosperms (flowering plants).

The fossilisation process of amber involves a progressive oxidation, where the original organic compounds gains oxygen, and polymerisation, which is an additional reaction where two or more molecules join together. This process produces oxygenated hydrocarbons, which are organic compounds made of oxygen, carbon and hydrogen atoms.  A peculiarity of amber is that it may perfectly preserve an organism in its original life position. 

What about the Yi Kwan Tsang Collection?

This collection consists of 115 amber samples from Chiapas, many of which contain abundant plant and animal fossil inclusions. The ambers were acquired over a 10-year period (~2004–2013) in San Cristóbal de las Casas, Mexico. The collection was displayed in 2015 at the Tucson Gem and Mineral Show and in 2016 at the Beijing International Jewellery Fair. 

FIGURE 1
Figure 1: This necklace from the Yi Kwan Tsang Collection contains amber beads from the San Cristóbal de las Casas area of Chiapas, Mexico, and was made by Francesca Montanelli (Lutezia Jewels, Stradella, Italy). Photo by Francesca Montanelli.

This article characterises Mexican amber from the Yi Kwan Tsang Collection using a variety of methods, including those not very common in gemmology, such as taxonomy studies and mass spectrometry, using techniques optimised for organic molecules. Some of the data was compared to those obtained from amber samples from the Baltic Sea and the Dominican Republic. 

The most important amber mines in Mexico are located in the area of Simojovel, but there are several deposits elsewhere in Chiapas State. They date back to the Late Oligocene/Early Miocene (23-13 Ma).

The area is characterised by three stratigraphic units that contain amber. From bottom to top, these are the La Quinta Formation (28–20 Ma), the Mazantic Shale (23–14 Ma) and the Balumtum Sandstone (16–12 Ma). Most of the amber deposits are associated with lignites, friable shales and deltaic clays in the sandstone. 

There are hundreds of amber mines in the tropical forest around Simojovel, and the amber is mined manually using hammers and chisels. 

The twenty-seven samples examined for inclusions were transparent and typically ranged from golden yellow, orange and orange-red to dark orange; a few pieces were dark brown, and some displayed a little natural green colouration. Internal features consisted of inclusions, as well as less common colour variations and small surface fractures. The fractures are probably related to stress associated with the polymerisation of the resin. 

All of the pieces were inert to short-wave UV radiation but displayed weak to strong fluorescence to long-wave UV. The RI values were constant (1.540), and they were similar to those of Baltic and Dominican amber. Average SG values were found to be homogeneous and relatively low (1.03). 

What about taxonomic classification, taxa and phylum?

Taxonomic classification is a hierarchical system used for classifying organisms to the species level. A taxa is a group in a biological classification, in which related organisms are classified. Phylum is a taxonomic ranking that comes third in the hierarchy of classification, after domain and kingdom.  Organisms in a phylum share a set of characteristics that distinguishes them from organisms in another phylum.   

What about arthropods?

The largest phylum of creatures on Earth without a doubt is Arthropoda, both in terms of number of species and in total number of individuals. There are nearly 1 million species of Arthropods, with over 90% of them being insects. 

The determination of the taxa of the botanical and animal inclusions was difficult because the species that lived in Chiapas during the Oligocene-Miocene were different from the modern ones.

The most important plant inclusions were represented by a petal and a leaflet of the genus Hymenaea, more precisely the species Hymenaea mexicana, which is now extinct. Animal inclusions were more common. They consisted of arthropods such as winged termites and a planthopper. Isolated termite wings were detected as well.

The presence of isolated termite wings is extremely rare and the planthopper species, Nogodina chiapaneca, has only been found in amber samples from Chiapas. It is an extinct species dated to the Middle Miocene, and it lived in a tropical or subtropical climate. The presence of an arthropod of the genus Ochlerotatus (female mosquito) also indicates an aquatic environment.  

Figure 8aFigure 2: (TOP) A flower petal inclusion of the species Hymenaea mexicana (Fabaceae family, Late Oligocene–Early Miocene; Poinar and Brown, 2002 and Calvillo-Canadell et al., 2010) is seen in this Mexican amber sample. The petal measures 1.1 cm long and 0.7 cm wide, and shows a narrow midrib base and basal laminar lobes with a central vein and branches of secondary veins. It appears completely glabrous (smooth). (MAIN ARTICLE IMAGE) The H. mexicana leaflet in this Mexican amber measures 3.3 cm long and 1.1 cm wide. The surface is glabrous and its veins are not visible in this view. Photomicrographs by V. L. Villani. 

FIGURE 11aFigure 3: A planthopper of the species Nogodina chiapaneca (order: Hemiptera, family: Nogodinidae; Solórzano Kraemer and Petrulevicius, 2007) is shown at the bottom of this sample. It measures 11 mm long, and displays a rounded head and a clearly visible thorax with one foreleg. The wings have several veins, but the scales are not preserved. This species is known only from Chiapas amber. Photomicrograph by V. L. Villani. 

FIGURE 12Figure 4: These winged termites and isolated wings (rare in Mexican amber) of the order Isoptera (reclassified as part of Blattodea) were likely trapped at the beginning of the wet season, when termites start to swarm and then shed their wings. The length of the wings is ~1.1 cm. Photo by V. L. Villani. 

What about X-ray powder diffraction?

X-ray powder diffraction (XRD), is an instrumental technique that is used to identify minerals, as well as other crystalline materials.The method is based on the scattering of x-rays by the crystals. X-rays are diffracted by each mineral differently, depending on what atoms make up the crystal lattice and how these atoms are arranged. An X-ray scan provides a unique "fingerprint" of the mineral.

Natural resin/amber is amorphous, so XRD analysis does not yield information on the amber itself but can identify mineral inclusions. XRD identified very small amounts of refikite and hartite, as well as calcite.  Calcite was identified by a diagnostic peak at 3.03 Å (or 29.8° 2θ) in the amber from Chiapas only.  Refikite and hartite have a composition similar to that of resin, but possess a crystalline structure.  They are probably associated with the polymerisation process of the resins. 

What about amber classification?

Amber can be classified according to two criteria: their place of origin, and their chemical composition. When succinic acid is present the amber is classified as succinate, when succinic acid is lacking it is considered as a resinite. 

Mass spectrometry was performed to deter­mine the presence of free succinic acid in the amber samples. Confirmation of succinic acid is obtained from the m/z 117 ion (the negative ion mass peak) corresponding to (M-OH)– of succinic acid. The mass spectrum of the Mexican amber did not show the m/z 117 ion, so the level of succinic acid in this amber was lower than the limit of quantisation (1 ppm by weight), classifying it as a resinite.

The Dominican sample showed a spectrum very similar to that of the Mexican amber, indicating the absence of succinic acid, while the m/z 117 ion was clearly identifiable in the spectrum of the Baltic amber sample.

What about Infra-red spectroscopy and the “Baltic Shoulder” in Baltic amber?

Infra-red spectroscopy is the most effective scientific method for identifying fossil resins.  With this technique, broad absorptions will be witnessed in Baltic amber in the 1260-1160 cm-1 range.  Those are assigned to C-O stretching vibration.  These features known as “Baltic Shoulder” are specific to Baltic amber and are related to the presence of succinic acid. 

Three wavenumber ranges that are important for amber characterisation are 3700–2000 cm–1, 1820–1350 cm–1 and 1250–1045 cm–1; these regions are associated with hydroxyl and carbonyl groups and to C=C double bonds. 

FIGURE 15Figure 15: FTIR spectroscopy of a Mexican (Chiapas) amber shows typical peaks at: 3600–3100 cm–1 (broad absorption band due to the O-H stretching vibration); 2965 and 2860 cm–1 (C-H stretching); 1740 cm–1 (C=O stretching, esters and acid groups); 1450 and 1380 cm–1 (C-H aliphatic hydrocarbons); 1260–1030 cm-1 (C-O stretching aromatic esters and secondary alcohols); and 846 cm–1 (C-C stretching of unsaturated olefins). 

The fossil inclusions observed in Chiapas amber in this study are consistent with a sub-tropical forest and FTIR spectroscopy was confirmed as a useful technique to determine the provenance of the amber samples.   

This is a summary of an article that originally appeared in The Journal of Gemmology entitled ‘Characterization of Mexican Amber from the Yi Kwan Tsang Collection‘ by Vittoria L. Villani, Franca Caucia, Luigi Marinoni, Alberto Leone, Maura Brusoni, Riccardo Groppali, Federica Corana, Elena Ferrari and Cinzia Galli 2017/Volume 35/ No. 8 pp. 752-765 

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

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

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

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

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

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

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.

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Birthstone Guide: Turquoise For Those Born In December

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...

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Understanding the Cat's Eye Effect in Gemstones

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 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

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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Jurassic Jet: A Look to the Past to Preserve the Future

With 2018 being the Year of European Cultural Heritage, Gem-A is excited to share Sarah Steele's important collaborative project between England and Spain to preserve and maintain traditional jet workings, which has recently been granted the European Heritage Seal.

Working with Spanish jet manufacturers and archaeologists, British gemmologist Sarah Steele FGA DGA of Ebor Jetworks is building an intercultural dialogue around the jet tradition to raise awareness of jet as a common and cultural heritage.


Sarah Steele FGA DGA image credit Gem-A©

She says: "We are really excited to have been credited with the 2018 Heritage Seal, as the cultural significance of jet cannot be underestimated. With a history of usage dating back at least 19,000 years, jet is one of the first gem materials to have been deliberately cut, shaped and polished. Personally, I am particularly excited as the award brings my research into Hydrocarbon Gemmology to a much wider audience, not only here in Europe but also further afield.

"Hydrocarbon Gemmology is currently beyond the remit of most gemmological education, but by opening an international dialogue on the subject, we hope to achieve our aim to legally protect culturally important materials such as Whitby Jet and Asturian Azabache."

READ MORE:  An Interview with GCDC Award Winner Jacqueline Cullen - Atomic Jet


Jet (Fracture) Image by Pat Daly

The importance of this initiative is reflected in the endorsement of the European Heritage Seal, denoting both the quality and value of the Jurassic Jet project. With jet and its tradition increasingly in danger of disappearing, the European Heritage Seal will provide crucial international visibility for this initiative.

The main aims of the project are to achieve official protection by the relevant authorities to guarantee the maintenance of the jet tradition, and to establish efficient regulation to prevent illicit commercialisation of materials sold as authentic jet and so preserve the integrity of the jet industry.

Read More: Whitby Jet: A Discussion of its Simulants 

Speaking on the importance of the international project, Sarah continues: "We have launched this exciting project with both a scientific and information vocation in mind. Alongside the historical, archaeological and geological research carried out by our collaborators, we will have other activities, both informative and formative for adults and children.

"These include exhibitions, workshops, talks and conferences. Cultural heritage has a universal value for us all and it is important that this is preserved and passed onto future generations."


.
 Top: jet from the Georgian Republic usually called 'gagate'. Left: Asturian Azabache. Right: a flat rectangular plank of Whitby Jet. Image Credit: Sarah Steele

Read More: Challenging Perceptions, meet the gem cutters thriving in Newcastle 

Collaborating with Andrea Menéndez (Archaeologist-Asturias, Spain), María Pérez González (Jet Manufacturer and president of Asociatión Azabache Jurásico de Villaviciosa, Asturias, Spain) this initiative aims to determine the characteristics and origin of jet in a scientific way, which will also help to create a seal of quality,  preserving the important position of jet in Europe’s historical and cultural heritage.

Sarah Steele will be speaking about this exciting project at the Jurassic Coast Symposium in York on 19th May 2018, which supports the Jurassic World Exhibition opened recently by Sir David Attenborough. Sarah will also be presenting her research at the Geologist Association Student Symposium this May in London, and has many other projected planned during 2018 in both Europe and the Americas.

For more on the Jurassic Jet project visit: www.azabachejurasico.com (in Spanish)

Visit Ebor Jetworks here

For more on The Year of European Cultural Heritage 2018 in the UK click here 

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

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

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

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

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

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

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

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

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 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

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


Additional Info

Read more...

Journal Digest: Radiocarbon Age Dating on Natural Pearls

Guy Lalous ACAM EG is on-hand to summarise some of the more in-depth articles from Gem-A's The Journal of Gemmology. Here, he explores an article on radiocarbon age dating of natural pearls from the Winter 2017 issue. 

This article describes how radiocarbon age dating can be adapted to the testing of historic pearls. The authors, Michael S. Krzemnicki, Laurent E. Cartier and Irka Hajdas, have developed their sampling method so that radiocarbon age dating can be considered as quasi non-destructive. The refined sam­pling process allows researchers to work with tiny amounts of nacre powder (~2 mg) taken from a drill hole without any damage to the outer surface of a pearl. In this article, pearls originating from a historic shipwreck were submitted to radiocarbon age dating. 

A small selection of pearls (approximately 2–8 mm diameter) from the Cirebon shipwreck was investigated for this study.
The pearls are shown on a historic map of the Java Sea, where the shipwreck was discovered. Photo by Luc Phan, SSEF.

The 10th century Nan-Han shipwreck was discovered accidentally in 2003 off the northern coast of Java, Indone­sia, near the city of Cirebon. The excavation of the ancient merchant vessels produced Yue ceramics, glassware and Chinese coins dating from the 10th century CE, jewellery, loose gemstones and also a number of carved gastropod shells and pearls. The thousands of glass fragments, and several unbroken blue and green glass objects found in the Cirebon shipwreck, undoubtedly originated from the Islamic Middle East. 

This indicates extensive trade in Southeast Asia along maritime routes at that time, which the Cirebon merchant vessel was a part of. This also supports a Persian Gulf origin for the pearls. The partly abraded and brown-to-grey altera­tions around the drill holes of these pearls suggests that they might have been in use for some time, strung on strands or set with metal lin­ings in jewellery before they sank in the vessel with the rest of its cargo. The coins and artefacts provided good evidence for a 10th century age of the shipwreck. 

What about X-radiography?

X-radiography is an imaging technique. X-rays are located beyond UV in the electromagnetic spectrum, where they have even shorter wavelengths and greater energy. Materials of low atomic weight allow x-rays to pass through easily and, therefore, appear dark on x-ray film, and those of high atomic weight block x-rays and appear white.

What about X-ray luminescence Computed Tomography?

X-ray luminescence is an emerging technology in X-ray imaging that provides functional and molecular imaging capability. This emission-type tomographic imaging modality uses external X-rays to stimulate secondary emissions, which are then acquired for tomographic reconstruction. This modality surpasses the limits of sensitivity in current X-ray imaging. 

What about EDXRF?

X-Ray fluorescence analysis using ED-XRF spectrometers is a commonly used technique for the identification and quantification of elements in a substance.

What about X-ray computed microtomography?

Seeing inside a material object, in three dimensions, is often crucial for proper characterisation, so that the link between microstructure and properties can be made. Micro-computed tomography or "micro-CT" is X-ray imaging in 3D on a small scale with massively increased resolution. It really represents 3D microscopy, where a very fine scale internal structure of an object is imaged non-destructively.

Fourteen pearls were analysed routinely by X-radiography and X-ray lumines­cence, as well as by EDXRF spectroscopy. Four of them were selected for X-ray computed microtomography (micro-CT) analysis. 

These 14 pearl samples (71742_A–N; approximately 2–8 mm diameter) from the Cirebon shipwreck were examined for this study.
They are partially abraded around their drill holes and show some brown to grey colour alterations. Photo by Luc Phan, SSEF.

Based on their X-radiographs, trace-element com­position and lack of luminescence to X-rays, the samples studied for this report were all saltwater natural pearls. The separation of natural from cultured pearls is mainly based on the interpretation of their internal structures. The radiography and micro-CT scans revealed that their internal structure main­ly consisted of fine ring structures typical of natu­ral pearls.

What about radiocarbon age dating?

The collision of high-speed neutrons produced by cosmic ra­diation with the nucleus of nitrogen results in the capture of a neutron and the expulsion of a pro­ton, thus transforming the 14N isotope into the radionuclide 14C. The radiocarbon, present only in trace amounts in the atmosphere, combines with atmos­pheric oxygen and forms radioactive carbon di­oxide, which is then incorporated into plants by photosynthesis and subsequently into animals via respiratory and metabolic pathways. As a consequence, the radiogenic 14C is incorporated into the endo- or exoskeletons (e.g. bones or shell structures) of animals.

After death, the lifelong exchange of carbon with the environment suddenly stops, resulting in a slow radioactive decay of 14C in the dead plants and animals. By measuring the ratio of radiogen­ic and stable carbon isotopes (14C/12C), it is thus possible to determine their age. The so-called half-life of 14C (that is, the time at which only half of the original 14C is still present in a sample and, as such, represents the constant rate of de­cay over time) is about 5,700 ± 40 years.

What about MICADAS?

The MICADAS is a mini carbon dating system through accelerator mass spectrometry. It is a two-step process. The first part involves accelerating the ions to extraordinarily high kinetic energies, and the following step involves mass analysis. The system allows radiocarbon analyses of ultra-small samples with great accuracy in only a couple of hours’ time. 

A pearl is a calcium carbonate (CaCO3) con­cretion formed by bio mineralisation processes in a mollusc—very much the same processes as for shell (exoskeleton) formation. As such, pearls (and shells) contain carbon, mainly the stable iso­tope 12C (as well as 13C) but also a small fraction of radiogenic 14C. The carbon used for the bio mineralisation of pearls and shells mainly originates from two very different carbon pools: (1) oceanic dissolved inorganic carbon; and (2) respiratory CO2, mainly stemming from food metabolism.

As such, the so-called marine reser­voir age effect may distinctly affect the resulting 14C ages of shells and pearls, especially in areas with upwelling of ‘old’ water.  Hence, a correction is required to take into account the geograph­ic location of the sample. The 14C/12C ratio was measured on three samples using the Mini Carbon Dating System (MICADAS).  

The calculated 14C age BP was corrected by apply­ing a marine reservoir correction that was based on values for the Java Sea location. These were estimated (mean-weighted) based on 10 data points in the vicinity of the sampling site. The result corresponds approximately to the end of the 10th century, which cor­relates well with the age stipulated for the coins, pottery and other artefacts found in the shipwreck. 

 Age determination can support evidence of historic provenance in the case of antique jewellery and iconic natural pearls. It can also be used to identify fraud in cases where, for example, younger pearls are mounted in historical jewellery items, or have been treated so that they appear older rather than having been farmed during the 20th century. 14C age dating can be used to obtain evidence to support a decision whether a pearl is of natural or cultured formation. This is because methods to commercially cultivate pearls from certain mollusc species only began during the 20th century.

This is a summary of an article that originally appeared in The Journal of Gemmology entitled ‘Radiocarbon Age Dating of 1,000-Year-Old Pearls from the Cirebon Shipwreck (Java, Indonesia) by Michael S. Krzemnicki, Laurent E. Cartier and Irka Hajdas 2017/Volume 35/ No. 8 pp. 728-736

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

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

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

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

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

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

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

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

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 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

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


 

Additional Info

Read more...

Survivors - The Geology of Diamonds

From the Spring 2018 issue of Gems&Jewellery magazine, Gem-A assistant tutor Beth West FGA DGA explores the remarkably epic journey of diamonds and how their characteristic strength is rooted in their archaic origins.

"In the deep glens where they lived all things were older than man and they hummed of mystery."
Cormac McCarthy, The Road

Carbon is the fourth most abundant element in the universe. It is one of life’s most important building blocks. We are made up of around 18% carbon. The diamond, however, is formed of pure carbon and bonded in such a way as to make it the earth’s hardest naturally occurring substance.

But these magnificent gems extend far beyond their beauty and durability; they carry whispers of the beginnings of our world.

How old is a diamond?

It has been proven that the oldest diamonds formed around 3.5 billion years ago in an age known as the Archean Eon. At this point, it is believed that the planet had only existed for around 1 billion years. The surface of the earth was still settling.

How are they formed?

The earth is formed in layers. The outer most layer is known as the crust and ranges between 6km and 40km deep. It is divided into the thicker continental crust, making up the landmass, and oceanic crust – the ocean floors. Beneath the crust is the mantle. It accounts for eight tenths of the earth’s volume and is predominantly composed of an igneous rock known as peridotite.

The upper most portion of the mantle and the crust are known as the lithosphere (‘rocky sphere’ in Greek). This part of the earth is rigid, whereas the deeper parts of the mantle are in a permanent state of convection as the rock melts and cools. At the centre of the earth, the liquid core encases the solid inner core – the 5500° C iron and nickel heart.

In the Archean Eon, as the crust shifted and split, portions of it found their place and settled. These archaic, unmoving pieces of crust are known as ‘cratons’. Under each craton is a root or keel of lithospheric mantle that can descend up to 300 kilometres deep. These keels are cooler than the neighbouring convecting mantle, at around 1200° C at its deeper points.

Diamond will start to form at around that temperature if the corresponding pressure is around 40000 atmospheres. That equates to a depth of around 140km. These deep lithospheric keels beneath the cratons, away from the chaos of the convecting mantle, were perfect safe-houses for a growing diamond.

Petra Diamonds' South African Mine, Finsch. Showing open put with subsequent block cave extraction, tunnels visible.
Image by Charles Evans FGA DGA.

Where did the carbon come from?

The carbon would have derived from either a primordial source (extant from the birth of the earth) or from material pulled into the mantle when the ocean floor was pushed beneath colliding continental crust.

The carbon would have been locked into compounds such as methane (CH4) or carbonates (CO3) travelling in melts or fluids around the convecting mantle. When these fluids passed through the mantle keel, they would have reacted to the peridotite, freeing the carbon from their compounds and allowing it to crystallise as diamond. It is in these deep portions of the keel that the oldest diamonds formed.

How did they get to us?

They resided in the keel for millions of years until, around the age of the dinosaurs (between an approximate age of 300 and 80 million years old), they were expelled from their plutonic residence via forceful, violent eruptions of magma produced deep in the mantle.

Kimberlite is the most abundant of the three types of known diamond bearing magma. This powerful magma blasted through to the surface producing a cone shaped hole called a ‘pipe’. Those diamonds that were carried up with the blast were left shaken but intact in the magmatic debris that packed the hole or were forced to travel with the weathering surface of the earth – often for great distances, in rivers or in glaciers, and for millions of years.

From the depths of the earth to the ring on our fingers, these stones have certainly proved their strength. So when we are drenched by the sparkle and marketed bling of these gemstones, it is perhaps worth remembering their remarkable journey.

This article originally appeared in Gems&Jewellery Spring 2018/ Volume 27/ 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: Diamond Crystal. Image by Pat Daly


The Fascinating History of Antique Turquoise Jewellery

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

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

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

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

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

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

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

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 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

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


 

Additional Info

Read more...

The 'Cat's Eye' Phenomenon: Exploring Chatoyancy

First published in the Spring 2018 issue of Gems&Jewellery, Harold Killingback FGA explores chatoyancy in sillimanite cabochons, an optical phenomenon where a band of light, known as a 'cat's eye', appears to hover above the surface of a stone, resulting in a striking lustre and colour.

Figure 1 shows a sharp cat’s eye in a sillimanite cabochon lit by a single point source (the sun) above the stone, i.e. from the same side from which it is viewed.

There is also a sharp ‘eye’ when the light comes up through the stone, toward the viewer, as shown in Figure 2. One can even see the ‘eye’ when the cabochon, lit from below, is viewed horizontally along the line of the stone’s major axis, see Figure 3.

 Figure 1. Epi-chatoyancy, plan view, lit by the sun.
In addition to the ‘eye’ line, there are reflections of the sun and of surroundings from the top surface of the cabochon.
All
 Image Credits: Harold Killingback FGA.

For these views, the single point of light was a fibre optic ‘pipe’, with an added tube 157 mm long and 10 mm in internal diameter, to fit the pipe. This acts as a collimator – a device that narrows a beam of particles or waves (including light).


Figure 2. Dia-chatoyancy, plan view.
Light from a fibre optic source below enters the stone through a suitably shaped hole in a black paper mask.
 As well as the “eye” line, the fibrous nature of the stone is visible.

It is less usual to see the effects in Figures 2 and 3 (dia-chatoyancy) than that in Figure 1 (epi-chatoyancy), partly because we normally admire gems when lit from above rather than from below, so we may simply miss seeing the effect.

Partly, also, because many chatoyant stones are too opaque to let much light pass right through them. Epichatoyancy, by contrast, can be the result of reflection from parallel inclusions immediately below the surface, and so the light path within the stone can be shorter, resulting in less absorption.

It helps, in this case, that the base of this cabochon is fairly smooth, rather than being left rough ground as is often the case, so more light from below can enter without being scattered.


Figure 3. Dia-chatoyancy, end view. The cabochon is resting on a glass slide so that fibre optic light can enter from below.
The background is illuminated by LED light, hence its blueness. Here, also, the fibrous structure of the stone can be seen, orientated at right angles to the bright line.

READ MORE: Insights and Reactions to De Beers' New Lab-Grown Diamond Jewellery Brand

Sillimanite, with andalusite and kyanite, is a polymorph of aluminium silicate. Its RI is in the range 1.654 -1.683 and DR 0.020 (1). A fibrous form, sometimes called Fibrolite, can exhibit chatoyancy due to its own structure. This example shows such a form.

The chatoyancy of the brown sillimanite from Orissa, India, is said to be due to ultrafine long and short ilmenite needles (2). The stone illustrated might well be from this source as the dealer said it was from India, but he could not be more precise.

I have not, however, been able to see any needles in this example. I put it near a strong magnet, but no attraction was detected. This stone measures 8.5 x 6.1 x 3.7 mm and weighs 1.75 ct.

Ray Diagram

The problem in drawing a ray diagram for chatoyancy is that one does not know where the relevant reflective surface is located within the stone, nor what angle it is orientated.

The solution is to work backwards along the exit ray, and forwards along the incoming ray, and then to see what has to happen where their paths cross if they are to be parts of a single ray.

The resultant diagram is shown in Figure 4, which represents a partial cross-section of the stone along its major axis as viewed from the side. In this example, I have chosen to examine the case of the dia-chatoyancy when the stone is viewed horizontally along the line of its major axis, as in Figure 3.

Arbitrarily, I have selected the horizontal ray leaving the cabochon at the point where the normal to the surface rises at 30º to the horizontal.

   
Figure 4. Ray diagram. Arbitrarily, an exit ray has been chosen, and the associated ray before refraction has been calculated.
Another arbitrary choice is shown for the entry ray.  The condition that these rays be one continuous ray is met by a reflective surface as shown.

READ MORE: The Geology of Diamonds

As the exit ray is horizontal, the angle of refraction, r, must be 30º. The incident angle, i, was calculated using Snell’s law, and an RI of 1.658. The resultant angle is 17.6º, and so the ray in the stone slopes up from horizontal at an angle of (r – i), which equals 12.4º in the case illustrated.

The arbitrarily chosen entrant ray is not refracted, as it is normal to the base. The angle between it and the exit ray just examined is 90 + (r – i). For these rays to be parts of a single path there must be a reflective surface where they meet. Let it be tilted at θ to the horizontal. As the incident ray at the reflecting surface is vertical, the angle of incidence is also θ, and the angle of reflection must be the same.

So 2θ = 90 + (r – i). In our example we get θ = 51.2º. This angle would be the same had I chosen any other ray in the vertical entrant beam.

We can repeat the calculation of θ corresponding to various exit points of horizontal rays from the stone as defined by the angle of the normal to the surface at these points. The results are shown below.

Angle of normal at exit point     

15.0    

30.0   

45.0   

60.0   

75.0

Angle of reflector                           

48.0    

51.2     

54.9   

59.2   

64.7

Figure 5 is included for fun, really, but it does illustrate the fact that multiple point sources produce multiple eye-lines. Here, there are but two sources and so two eyes. In the limit, a cloudy sky consists of infinite point sources and produces, not any lines at all, but so many that no individual line can be distinguished and the stone reflects an even glow.


Figure 5. Bi-dia chatoyancy. The white line is produced by a fibre optic incandescent light from below the cabochon.
The blue line is from a LED torch, also from below, but slightly to one side of the other source.
The camera was set to correct for the red cast of tungsten light, so the LED ray looks very blue by comparison. Note the fibrous nature of the stone.

Conclusions

I have calculated the angles of reflector surfaces for only one direction of view and only one of sillimanite’s two values of RI. These reflector angles could all be provided if the reflecting inclusions were roundish in cross-section, whether hollow tubes or fibres.

If, however, the inclusions are crystalline and polygonal in cross-section, one is forced to the conclusion that the orientation of the needles about their long axis must be random, in contrast to the fact that this axis must, in all cases, be orientated in the direction dictated by the structure of the material.

An alternative explanation is given by Moon and Phillips (3). They ascribe the effect as being due to Fraunhofer diffraction, applying Babinet’s Principle of Complementary Apertures. The needles can then be regarded as apertures of the same size. The crosssection of the needles is then of no consequence.

This paper has also demonstrated that where, as here, it is not possible to trace a ray from start to finish, one can trace a known emergent ray backwards as far as possible, and then trace a known entry ray forward. If these rays cross, one can deduce what could unite these rays into a single path.

References

1. Identification of Gemstones, pp 254-255. O’Donoghue and Joyner.

2. Photoatlas of Inclusions in Gemstones, Vol. 3, p 626. Gübellin, E. and Koivula, J. I.

3. A. R. Moon and M. R. Phillips, Schweiz. mineral. petrogr. Mitt. 64, 329-334, 1984.

This article originally appeared in Gems&Jewellery Spring 2018/ Volume 27/ 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: Bi-dia chatoyancy in cabochon. Image Credit Harold Killingback FGA. 


The Fascinating History of Antique Turquoise Jewellery

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

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

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

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

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

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

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

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 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

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


 

Additional Info

Read more...

Fake News? Discovering 'Alternative Facts' in Gemmology

From the Spring 2018 issue of Gems&Jewellery, Rui Galopim de Carvalho FGA DGA explores how ‘alternative facts’ have resulted in an informal nomenclature that permeates the world of gemmology. Here, he offers some examples of these long-standing quirks in terminology.

In gemmology there are a number of trade names and expressions that lack accuracy. However, written or verbal tradition has given them a wide visibility and many have become part of our trade’s informal nomenclature.

Here are a few examples. This article does not intend to set standards or correct any existing article or gemmological text. This review has resulted from the careful reading of multiple books and journals in the course of normal study processes and peer review editing to verify or validate information.

More than pointing out apparent mistakes or erroneous information, this approach has shown there is a balance between purist or scientific lexicon and the more trade-orientated nomenclature, which is characteristic of gemmology that serves an industry and its consumers.

READ MORE: The 'Cat's Eye' Phenomenon - Exploring Chatoyancy 

It also demonstrates that there are terms that emerge from colloquial tradition and not necessarily from academia. For this article, a selected number of situations have been chosen to illustrate the misuse of expressions and names, although in some cases, tradition wins over picky nomenclature.

These are ‘alternative facts’ in the sense that, for the more conservative and orthodox reader, they can be considered ‘fake news’.

FLAME FUSION ‘SYNTHETIC’ SPINEL

One of the most popular artificial products that gemmologists learn how to identify in their education is the flame fusion, or Verneuil, synthetic spinel.

These have been around for almost a century and were produced in many colours (except red) to imitate, not natural spinel, but rather other gem materials such as diamond, aquamarine or blue sapphire to name a few (O’Donoghue, 2005). 

The gem and jewellery community, and almost all literature, simply describes these products as ‘synthetic spinel’ (O’Donoghue, 2006, Matlins, 2003, Liddicoat, 1993, Hodgkinson, 2015).


A ca. 1960 Portuguese brooch in 19.2k gold with a flame fusion blue ‘synthetic spinel’. According to trade regulations, one could not call the material a ‘synthetic’ but rather an artificial stone.
Photo: Carlos Pombo Monteiro © Arquidiocese de Évora/ Fundação Eugénio de Almeida.

The trade, however, has a very strict definition of ‘synthetic’ and CIBJO – The World Jewellery Confederation – defines synthetic stones as “artificial products having essentially the same chemical composition, physical properties and structure as that of their naturally occurring counterparts” (CIBJO Gemstone Book, 2016).

It happens that every gemmologist knows that the gemmological properties of natural spinel differ slightly from the properties of the flame fusion counterpart, due to the fact that they do not have the same chemical composition, with a different alumina to magnesia ratio (Al2O3 / MgO), that is 1/1 in natural spinel and usually 3.6/1 in the flame fusion product (Rinaudo, 1997).

READ MORE: Birthstone Guide - Pearls for those born in June

In strict observation of the CIBJO rules, we could not call these products ‘synthetic spinels’ as they do not meet the criteria for a synthetic stone.

This is, however, a typical case when a verbal or written tradition overtakes the formality of a nomenclature rule. Despite the noncompliance with the trade standards, it is widely accepted and tolerated that these products can be named, tagged and traded as ‘synthetic spinel’.

MARCASITE AS A GEM MATERIAL

In the gemmological world we refer to marcasite as an opaque, golden material with a metallic lustre, often cut in very small and simple rose-type pieces. Its first record goes back to the 18th century (Pouget, 1762) with its heyday as a gem material in the 1930s (Bartlett, 1997). The name marcasite drives from the Arabic or Moorish word used to describe pyrite and other minerals (Anthony, 1990).

As an actual fact, the name shouldn’t be marcasite, but pyrite as this material is the well known cubic iron sulphide (FeS2). Today, every major text book acknowledges the fact that the material is pyrite and that marcasite is an accepted trade name in the jewellery community (Webster, 1994, Hodgkinson, 2015).

Marcasite is in fact the IMA — International Mineralogical Association’s approved name for a distinct mineral that has no use in jewellery whatsoever, occasionally causing confusion to a more scientifically-educated public.

A ca. 1940 silver pin set with a paste and small round shaped marcasites, known as pyrite in the scientific community.
Photo: 
Carlos Pombo Monteiro © Arquidiocese de Évora/Fundação Eugénio de Almeida.

Marcasite and pyrite are two distinct materials in spite of being polymorphs of iron sulphide, with marcasite crystallising in the orthorhombic system and pyrite in the cubic system (Klein, 1993).

These polymorphs were defined as separate mineral species in 1845 when marcasite was proposed as a new species (Heidiger, 1845) but some authors and museums reportedly had difficulty in separating them (Bannister, 1932), a task that was greatly solved by Bragg in 1914 with the introduction of X-ray diffraction in mineral identification.

READ MORE: Investigating Ammolite  

In the jewellery world, the word marcasite kept being used in the traditional way despite the acknowledgment of its true mineral classification as pyrite, which makes this another typical case of an erroneous name kept due to trade tradition (Bartlett, 1997).

‘ORGANIC’ GEMS?

Since the dawn of gemmological education in the second quarter of the 20th century, gem materials have been commonly organised into separate categories, like diamonds, coloured gemstones and organics.

Within organics we see a list of gem materials that originate from the activity of living organisms, e.g. ivory, bone, coral, tortoiseshell, pearl, mother-of-pearl, shell, horn, corozo (vegetable ivory) and copal just to name the most important ones (Pedersen, 2004).


Pearls, like these natural colour bead-nucleated cultured pearls from Fiji, are examples of gem materials that should be named biogenic and not organic due to their composition.
© J Hunter Pearls Fiji.

It happens though that the word ‘organic’ has specific meanings, rather than simply being the broader statement of material generated by a living organism (e.g. a carbon based compound).

Moreover, some of the gem materials grouped as organics are not, in any sense, organic in composition and that is the case of precious corals, pearls, cultured pearls, mother-of-pearl and shell.

The major composition of the materiais is bio-mineralised calcium carbonate in aragonitic and/or calcitic structures. Carbonates, as crystal matter, are strictly speaking considered inorganic matter, not organic (Strack, 2006).

At the 2016 CIBJO Congress, these arguments were discussed and there was a consensus that a better word to describe gem materials that originate from living organisms would be ‘biogenic’, literally meaning that they result from biological activity. 

A full list of references is available upon request. All Image Credits: Rui Galopim de Carvalho.

This article originally appeared in Gems&Jewellery Spring 2018/ Volume 27/ 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: A ca. 1960 Portuguese brooch in 19.2k gold with a flame fusion blue ‘synthetic spinel’. According to trade regulations, one could not call the material a ‘synthetic’ but rather an artificial stone. Photo: Carlos Pombo Monteiro © Arquidiocese de Évora/ Fundação Eugénio de Almeida.


The Fascinating History of Antique Turquoise Jewellery

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

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

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

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

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

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

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

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 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

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


 

Additional Info

Read more...

An Afternoon in Antwerp's Historic Diamond District

Gem-A Member Carmen Garcia-Carballido MSc., L. Geology, EurGeol FGA DGA, explores Antwerp's historic diamond district - the Diamantkwartier.

Antwerp in Belgium is famous for diamonds. In 2017, it traded approximately 234 million carats. Over 80% of rough diamonds are purchased in Antwerp, where half the world’s 'Kimberley Certificates' are issued, and the square mile of its 'Diamond Quarter' hosts 1,600 diamond dealers, employing over 30,000 people. Diamond, not beer, is Belgium's top export.

Antwerp History 

In the 16th century, Antwerp was the world’s biggest trade centre, with the diamond trade to and from the city having been recorded since 1447.

Port House of Antwerp, Belgium. Designed by Zaha Hadid, which reinterprets Antwerp's moniker as the city of diamond.
Image Credit: pixabay
 

But how are diamonds traded? It started in the coffee houses near Centraal Station. In the days before security cameras, merchants had to move fast to avoid being mugged, so the 'Diamond Quarter' sprang up just next to the station, which is still a convenient location for tourists and dealers. Nowadays, vetted and registered members can trade at one of Antwerp’s four diamond bourses; there is no other city in the world with so many, and there are only 30 Diamond Bourses worldwide. Some bourses specialise in cut diamonds, others in rough or industrial diamonds and some are even on the sites of the old coffee houses. 

Antwerp Centraal Station. Image Credit: pixabay 

The Antwerp World Diamond Centre (AWDC), a private foundation representing the sector in Belgium, maintains Antwerp’s position as a world diamond centre. Antwerp's main diamond bourse was founded in 1904 and by WWII it had 1,645 members, however, at the war’s end just 335 remained. The AWDC hosts the 'Diamond Office' founded in 1945 to encourage Jewish diamantaires to return to Antwerp, and it also now handles all diamonds entering the city. 

Dealing in diamonds is an expensive business. A tender facility located within the AWDC is where mining companies sell their rough diamonds. Each buyer bids in a sealed envelope and the stones are sold to the highest bidder. Specialised banks give fast credit to registered trading companies and all transactions are by bank transfer to comply with anti-fraud laws.Although diamond dealing is based on trust, diamond bourse members must comply with strict rules.

History of Antwerp and Diamond Cutting 

Antwerp has a rich history of diamond cutting. Marcel Tolkowsky, a native of Antwerp, refined the brilliant cut early in the 20th century. His nephew, Gaby Tolkowsky, cut some of the world’s most famous diamonds: the Centenary (273.85 ct) and the Golden Jubilee (545.7 ct). Until the early 1970s, most rough diamonds traded in Antwerp were also cut there.

Nowadays, rough is exported to India or China for cutting and polishing and re-imported for sale in Antwerp, hence the saying: "Almost every diamond in the trade travels though Antwerp at least once." 

 Figure 1

I visited the fantastic showroom at DiamondLand (Appelmansstraat 33) and saw cutters and polishers at work. Figure 1 shows a crossworker using the traditional equipment, including; the scaife, a horizontal cast iron disc which rotates at 3,200 rpm and is impregnated with diamond dust and oil; an adjustable dop which holds the diamond; and the tang, a tripod which holds the dop. 

 
Figure 1a

The tang is held by the crossworker who exerts pressure onto the diamond while cutting and polishing. It is lifted frequently to inspect the diamond under the loupe, and here two diamonds are being worked at the same time (Fig. 1a).

Royal 201 Diamonds

DiamondLand also showed me some Royal 201 cut diamonds. This modification of the round modern brilliant cut has been on the market circa 2004. It has 65 crown and 40 pavilion facets plus 96 micro facets on the girdle. The Royal 201 cut exhibits higher brilliance and fire than the modern brilliant cut and this can affect colour grading, making a Royal 201 cut stone appear a higher colour grade than it really is. It has different proportions to the modern brilliant cut; the crown appears bulgier, so it is important that diamond graders and valuers identify this cut and put it in its context.

Before leaving the Diamond Quarter, I paid a visit to HDR Antwerp, a famous institution for diamond certification, training, and instruments (both gemmological and for diamond manufacture and screening) where I had the opportunity to see their range of state-of-the-art devices. So, Gem-A members, if you happen to find yourselves in Antwerp, take a moment to explore its rich diamond history.

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.

Additional Info

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110 Years of Gemmology

It all started with an idea...

Manchester, England, 1908
110 years ago today, on July 6 1908, Samuel Barnett a jeweller from Peterborough, stood up at a gathering of the National Association of Goldsmiths to propose an idea: to offer lessons and examinations in gemmology to support the jewellers’ industry. 

The UK’s leading goldsmiths and jewellers supported the idea and created an official committee to advocate gemmological education. In that moment, Barnett established the UK as the world’s first provider of gemmological education, and became the father of what would one day become Gem-A. As another Gem-A founding father, Basil Anderson, noted many years later, Barnett’s proposal "marked the beginning of organised gemmology, not only in this country, but in the whole world".

 
G.F Herbert Smith

This was an exciting time of innovation in the gemmological world. The years building up to Barnett’s proposal had already seen the arrival of the Steward Refractometer in 1905, followed by the Goniometer and Spectroscope in 1907. Renowned mineralogist Dr G.F Herbert Smith was also developing his ground-breaking book Gemstones, released in 1912, offering the first textbook on gemstones with full instructions on how to use specialist equipment. While the gems and jewellery industry was an ancient trade, this equipment enabled jewellers to now look inside their stones, and these years mark the first advances in practical gemmology.

London, 1913
Within five years of Samuel Barnett’s proposal the first gemmological examinations were held, set and marked by Herbert Smith, with Barnett himself receiving the first ever Diploma in Gemmology. 

Since 1913, gemmology has gone from strength to strength, with the continued ethos of serving the industry through championing access to gemmological education.

In 1938 we officially became the Gemmological Association of Great Britain, and over the last century we have seen a prestigious line of Gem-A presidents, including internationally renowned gemmologists, inventors and even Nobel Prize winners. Over the next coming months our 'Heritage Series' will showcase these Gem-A Greats and their contributions to the advancement of gemmology and the wider scientific community.

From an idea in 1908, today Gem-A’s Gemmology and Diamond Diplomas are taught in 40 Accredited Teaching Centres across the world and our FGA and DGA members are internationally recognised by the industry.

Between now and the Gem-A Conference in November we will be celebrating the last 110 years of gemmology and our proud history of being the world’s first provider of gemmological education. So keep an eye out for the latest 'Heritage Series', where we will explore our illustrious founders, including Herbert Smith, Basil Anderson, and Sir Lawrence Bragg.


Gem-A Graduates 2017

 

If you would like to join us in celebrating 110 years of gemmology education click here and register for the Gem-A Conference 2018.

If you are a Gem-A Member or Student you will receive an email with an access link, if you haven't received it please contact membership@gem-a.com.

 


The Fascinating History of Antique Turquoise Jewellery

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

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

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

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

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

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

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

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 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

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


 

Additional Info

Read more...

Journal Digest: Delve into the Colours of Rainbow Lattice Sunstone

Guy Lalous ACAM EG returns with his latest Journal Digest, which summarise a scientific article from Gem-A's Journal of Gemmology. Here, he explores an article on rainbow lattice sunstone from Australia featured in the Spring 2018 issue, Volume 36 No. 1. 

The feldspars are a family of silicate minerals which occur in igneous rocks. They contain variable amounts of Na, K and Ca and are divided in two solid solution series: plagioclase (albite – anorthite) and alkali feldspar (orthoclase – albite). Both orthoclase and plagioclase boast of a sunstone feldspar variety, however, the name ‘sunstone’ refers to the gem’s appearance rather than to its chemical makeup.

What is aventurescence and adularescence?

Aventurescence, is a ‘sparkly, metallic-looking luster caused by flat, reflective inclusions’ (GIA). Adularescence is the term applied to gems exhibiting a sheen or schiller effect caused by the intergrowth of two different feldspars, such as moonstone. The colours seen in such material depend on the thickness of the layers involved, with the thicker ones giving rise to colours from the red end of the spectrum and the thinner ones colours from the blue end.

Figure 1: Rainbow lattice sunstone displays conspicuous colourful patterns that are produced by light reflecting at a specific angle from inclusions.
The gold ring on the left contains a 6.17 ct sunstone and the polished fragment on the right weighs 15.00 ct. Courtesy of Rainbow Lattice; photo by Jeff Scovil.

A rare gem feldspar known as rainbow lattice sunstone exhibits both aventurescence and adularescence, with the added presence of oriented elongate and triangular mineral platelets. The authors (Jia Liu, Andy H. Shen, Zhiqing Zhang, Chengsi Wang and Tian Shao) examined this sunstone using microscopy, electron microprobe and XRD analysis, magnetic measurements, SEM-EDS and Raman spectroscopy.

 Figure 2: The six samples of rainbow lattice sunstone obtained for this study display a combination of optical effects
including adularescence (e.g. sample 1), aventurescence (see samples 1 and 6, in particular) and a rainbow lattice effect, which can be seen using different lighting conditions and directions.
The samples weigh 0.29–3.57 g. Composite photos by J. Liu.

Rainbow lattice sunstone is found in the Harts Range, north-east from Alice Springs, Northern Territory, Australia. The Harts Range comprises a complex assemblage of granite gneiss, marble, calc-silicate, amphibolite, psammite and pelite that have been metamorphosed to upper amphibolite to granulite facies (Huston et al., 2006). The metamorphosed sedimentary rocks are intruded mainly by granite, granodiorite and metamorphosed mafic rocks of uncertain origin.

The igneous rocks are generally associated with widespread metasomatic granitisation. The granodiorite in the Bruna gneiss unit contains pegmatites in which K-feldspar occurs, and the mining area is crosscut by quartz veins and pegmatite outcrops.


Figure 3: The adventurescence phenomenon in the sunstone is produced by pseudohexagonal reddish brown platelets of hematite.
A) exhibits sparkling appearance in reflected light. B) Images taken from sample 1. Photomicrographs by J. Liu.

The typical aventurescence of sunstone can be seen with magnification. In their analysis, Liu et al., found that the scattered reddish-brown platelets showed pseudohexagonal and rhomb-shaped morphology. The lattice-forming inclusions in the sunstone consisted of orangey brown to black elongate and triangular plates. 

The orangey brown ones displayed colourful reflections when viewed with oblique pinpoint lighting. Some of the samples displayed obvious adularescence when observed using various incident light angles. Gemmological testing of the rainbow lattice sunstone revealed average RIs of 1.518 to 1.540, and an SG of 2.58, which are consistent with those of orthoclase.

Scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS)

As noted by Katrin Field Inc., ‘viewing three-dimensional images of microscopic structures only solves half the problem when analysing samples. It is often necessary to collect more than imaging data to be able to identify the different elements in a specimen.’

SEM images of the black inclusions of magnetite in rainbow lattice feldspar.
Yellow line designates the remaining areas of magnetite, while the dashed red lines show the inferred outline of the original platelets. Images by J. Liu.

Utilising the SEM-EDS Microscope system, we can examine micro-scale and nano-scale features with magnification up to 300,000x and detect chemical composition. 

The black platy, elongate or triangular inclusions consisted of thin sheets with nanometer-scale thickness. Qualitative SEM-EDS analysis revealed that these inclusions contained Fe and O, but no Ti was detected in the present study.

A tiny fragment of the sunstone containing only one black inclusion that was strongly attracted to a Nd-Fe-B magnet, which proved that the black inclusion consisted of an oxide of iron that possessed strong magnetism.  The presence of magnetite as the ferromagnetic material is consistent with the SEM-EDS analysis. 

Electron Microprobe Analysis

Electron microprobe analysis is an analytical technique that is used to establish the composition of small areas of a specimen. As Dr. Nilanjan Chatterjee of MIT’s Electron Microprobe Facility notes, this method is non-destructive and utilises X-rays excited by an electron beam incident on a flat surface of the sample. 

This article found that the quantitative chemical compositions and end-member components of the host feldspar, analysed with the electron microprobe, showed 96% orthoclase and 4% albite. 

The black to orangey brown, platy, elongate and triangular inclusions that produce the rainbow lattice effect are shown in both transmitted (a, b) and reflected (c–f) light. Photomicrographs by J. Liu.

X-ray diffraction (XRD)

XRD is an instrumental technique that is used to identify minerals, as well as other crystalline materials. The method is based on the scattering of x-rays by the crystals. In a 2014 article published on XRD Analysis: Principle, Instrument and Applications, M.S. Pandian observed how: ‘X-rays are diffracted by each mineral differently, depending on what atoms make up the crystal lattice and how these atoms are arranged....’ An X-ray scan ‘provides a unique "fingerprint" of the mineral’. In the sunstone analysed by Lui et al., the XRD pattern of the host feldspar identified it as orthoclase (Or96Ab4).

Raman spectroscopy

Raman Spectroscopy is a testing technique using infrared, visible or ultraviolet light to identify different specimens. When this monochromatic light is applied at a specific frequency via a laser, the Raman spectrometer detects the re-emission of photons.

Most of the photons pass through the material, but some interact with the molecules and modify the vibration of the atomic bonds. Most photons are scattered with no change to their energy, but a small number of photons lose energy to the molecules, and even fewer gain energy. This energy difference (Raman effect) is a distinctive feature of particular molecules, and can be used to identify them.

As such, the Raman effect is different for each material, based on its molecular structure and we can use individual emission spectrums to identify different gemstones. This is because a number of energy values are associated with gem species, and these are expressed by waves per cm and are viewed as a series of peaks. These peak patterns form a database for us to identify not only gemstones, but to identify inclusions and treatments.


 This representative Raman spectrum of the host feldspar.

Raman spectrum of the host feldspar showed peaks at 455, 474 and 513 cm–1 which is proof of its identity as orthoclase. The main Raman shifts of the reddish-brown platelets causing the aventurescence and the orangey brown lattice-forming inclusions were 226, 245, 297, 411, 500, 612 and 1319 cm–1, which match with hematite. The main Raman shifts of the black lattice-forming inclusions were 303, 538 and 664 cm–1, which fit nicely with magnetite.

Conclusions 

Sunstone inclusions may be composed of hematite, ilmenite, magnetite, native copper or goethite. The appearance of the aventurescence phenomenon depends on the size of the inclusions. Small particles produce a reddish or golden sheen, while larger inclusions create an attractive, glittery appearance.

The lattice appearance displayed by rainbow lattice sunstone is created by inclusions of hematite and magnetite. These minerals form very thin blades that occur within planes of a single orientation at different levels in the feldspar (like pages in a book).

Platelets of hematite also produce aventurescence. Viewed with reflected light, the aventurescence is illuminated from one direction, while the colourful lattice effect appears when the lighting is shifted to a different angle.

The magnetite and hematite predominantly form triangular shapes or elongate blades with terminations that are parallel to the triangular directions. The magnetite inclusions in many cases have oxidized to hematite, corresponding to the iridescence or rainbow effect across the lattice patterning. In contrast, the unaltered magnetite is black with a metallic sheen.

Unfortunately, there is not much of this material available in the market.

This is a summary of an article that originally appeared in The Journal of Gemmology entitled ‘Revisiting Rainbow Lattice Sunstone from the Harts Range, Australia’ by Jia Liu, Andy H. Shen, Zhiqing Zhang, Chengsi Wang and Tian Shao 2018/Volume 36/ No. 1 pp. 44-52

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

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

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

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

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

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

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

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

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 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

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


 

Additional Info

Read more...

Sir Henry A. Miers - Gem-A's First President

'Curiouser and Curiouser', said the Gemmologist

On July 6, Gem-A celebrated the anniversary of 'organised gemmology education', the idea proposed by Peterborough jeweller and one of Gem-A's founding fathers, Samuel Barnett. For the second instalment of our Heritage Series we turn to Gem-A's very first president, Sir Henry A. Miers F.R.S, the eminent mineralogist and crystallographer who became Gem-A president in 1932.

In his lectures for the Royal Society in 1896 on ‘Precious Stones’, Henry Miers aimed to highlight the importance of considering, not just the history or artistic interest of gemstones, but some of their more curious properties.

By examining their refractive index and specific gravity, Miers demonstrated how instruments such as the goniometer, refractometer, dichroscope, and polariscope helped to determine the identity of gemstones beyond opinion to scientific proof: ‘the methods are those of physical science – and they are accurate’ (Miers 1896, Scientific American, 17309)


From the 'Precious Stones' article  (Miers 1896, Scientific American, 17309)

Observing the number of serious mistakes made in the jewellery trade in the 1890s, Miers despaired that ‘the jeweller’s trade stands almost alone…in ignoring the aid of physical science’ and in these lectures, published in Scientific American, he championed the ‘absolute necessity of accurate scientific knowledge’ to identify gemstones (and their imitations).

Graph detailing SG and RI from the 'Precious Stones' article  (Miers 1896, Scientific American, 17309)

In just over a decade’s time in Manchester July 1908, Samuel Barnett would propose the establishment of organised gemmological education to the National Association of Goldsmiths, and Miers’ call for applied gemmology in the jewellery industry would become a reality.

Read more: 110 years of Gemmology

For Miers, those fortunate enough to delve into the world of gemmological science were intrepid explorers, and in their ‘attempt to explain all these curious properties, will find themselves in a most fascinating field of discovery and speculation.’ (Miers 1896, Scientific American, 17309)

It was a world that Miers remained in for his entire life.
A King’s Scholar of Eton College, the young Henry went to Trinity College, Oxford, on a classics scholarship, before transferring to mathematics. From Oxford, Miers joined the Mineral Department of the British Museum (Natural History) under Lazarus Fletcher in 1882 and – like many of his Gem-A successors – went on to become Keeper of the Minerals.

At the British Museum, Miers arranged the mineral gallery and the crystallography catalogue, while also lecturing in crystallography at Central College, South Kensington, and publishing his research on precious stones and the morphology of various minerals.


Gem-A's collection of Miers' work

Remaining in the fascinating field of discovery that is gemmology, Miers was offered the Chair of Mineralogy in 1895 at Magdalen College, and on his return to Oxford he improved their laboratory and the University’s mineral exhibition. Miers was also made a fellow of the Royal Society in 1896 and in 1902 published his seminal work Mineralogy: an introduction to the scientific study of minerals, before becoming president of the Mineralogical Society for 1904/5.

Read More: Gem-A History 1908-Present

In 1912 he was knighted, and in 1915 became the Vice-Chancellor and Professor of Crystallography at Manchester, which under Ernest Rutherford became a hub for nuclear physics and crystallography, attracting the likes of the Nobel Prize Winner Sir Lawrence Bragg - who likewise would go on to become Gem-A president!

Sir Henry Alexander Miers, Gem-A's President 1932-37.
National Portrait Gallery, London, Creative Commons.

In 1926, Miers returned to London and became a trustee of the British Museum. He was appointed to the Royal Commission for National Museums and Galleries, a role that took him around the UK and the world: the Carnegie UK trust invited him to report on museums across Britain, and then for the Carnegie Corporation in New York. He went on to Canada and British Africa in 1932. It was at this time that Sir Henry was approached to become the first president of the (then) Gemmological Association, a post he held until 1937.

Printed Works of Gem-A Greats featured in our 2018 Heritage Series. 

Sir Henry Miers died peacefully at home on 10 December 1942, aged 85, as arguably one of the first trailblazers of gemmology. He was held in such high esteem that it was the equally renowned Dr Herbert-Smith who wrote his obituary in Nature. It is to Herbert-Smith we will turn to in our next instalment of Gem-A’s ‘Heritage Series’.

If you would like to join us in celebrating 110 years of gemmology education click here and register for the Gem-A Conference 2018.

If you are a Gem-A Member or Student you will have received an email to book member or student rates, if you haven't received it please contact membership@gem-a.com.

Cover Image: Sir Henry Alexander Miers by Lafayette, whole-plate film negative, 30 May 1929, NPG x69585 © National Portrait Gallery, London, Creative Commons. 


The Fascinating History of Antique Turquoise Jewellery

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

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

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

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

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

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

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

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 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

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


 

Additional Info

Read more...

Dr Herbert Smith: Innovator, Inventor, Gem-A President

Dr Herbert Smith was Gem-A President from 1942 until 1953. He was integral in the development of gemmology for the jewellery trade and had an extensive list of accomplishments throughout his career and tenure as president: 
- He developed the Herbert Smith refractometer which, as Noel Heaton noted, improved the instrument beyond recognition and provided the industry with a means to determine the refractive index of a gemstone in a matter of seconds (without even needing to remove it from a setting).

From Nature 25 May 1911 

- He not only discovered a new mineral (paratacamite), but also has one named after him (Herbertsmithite).

- His seminal work Gem-Stones 1912 is well known to students and jewellers alike, as the first text book on gemmology with full instructions on how to use specialist equipment.

- Maybe you are are Gem-A student or graduate who has studied in the Herbert Smith room here at Gem-A HQ in London.

- You may have even bought a postcard featuring collections from the British Museum – this idea was born from Herbert Smith and is a tradition that continues today.

READ MORE: 110 Years of Gemmology

Mineralogy at the British Museum (Natural History)
Like Henry Miers before him, the young Herbert Smith went to Oxford – specialising in mathematics and physics, and then likewise went on to join Sir Lazarus Fletcher’s Department of Mineralogy at the British Museum (Natural History) in 1897 where he soon specialised in crystallography and in the use of instruments to identify faceted gemstones.

Through this work he invented the three-circle goniometer and designed an updated refractometer which, in doing so, ‘put in the hands of jewellers an instrument that all could use effectively with very little difficulty’ (W. Campbell-Smith). 

Demonstration of the Herbert Smith Refractometer in the 1912 'Gem-Stones'

In 1912 Herbert Smith published the pioneering work Gem-Stones, which was the first systematic approach to gemmology, and importantly, accessible gemmology. As he noted in his preface:

‘If this book be found by those engaged in the jewellery trade
helpful in their everyday work, and if it wakens in readers generally
an appreciation of the variety of gems, and an interest in the wonderful
qualities of crystallised substances, I shall be more than satisfied’

(Gem-Stones 1912: viii)

READ MORE: Gem-A's first President: Sir Henry Miers

Legacy at Gem-A
Maintaining this purpose, when the National Association of Goldsmiths enacted Barnett’s 1908 proposal for gemmological examinations, it was Herbert Smith who set and marked the first Gemmology Diploma, he remained at the core of the educational committee that became the Gemmological Association in 1931. 

The Gemmology Diploma examination from 1933, marked by Herbert Smith

To this day Gem-Stones is a gemmological treasure and its multiple editions have involved contributions from some of the other stalwarts throughout Gem-A history including: R.Webster, B.W Anderson, G.F Andrews and G.F. Clarringbull.

Various editions of Herbert Smith's 'Gem-Stones' from the Gem-A Collection

Herbert Smith went on to become Gem-A president in 1942, succeeding the Nobel Prize Winning crystallographer Sir William Bragg, and remained so until his death in 1953.

READ MORE: Journal Digest: Delve into the Colours of Rainbow Lattice Sunstone

During this time he was also – like many of Gem-A's previous Presidents – Keeper of the Minerals at the British Museum (NH), and he spent much of his professional life in service to the Museum. He championed inclusivity and outreach through his work with Gem-A, the Civil Service Arts Council, the Society for the Promotion of Natural Reserves, and the Wild Plant Conservation Board. He was also a part of the British delegation to the International Conference for the Protection of Nature at Bruunen in 1947.

Handwritten dedication by Herbert Smith in his 'Gem-Stones' to his daughter Jeanne
May 1912

He was a fellow of the Royal Astronomical Society, a member and vice-president of the Mineralogical Society, a fellow of the Geological Society and a member of the British Association. To top it all off, in 1949 he was awarded a CBE.

It is fair to say that without Herbert Smith, Gem-A and gemmology as we know it today would not have been possible. He was a pioneer of gemmology for the jewellery industry, a Gem-A examiner from 1913 to 1951 and he cultivated knowledge throughout his life and shared it with others.

READ MORE: Gem Empathy Competition Returns for IJL 2018

If you would like to join us in celebrating 110 years of gemmology education click here and register for the Gem-A Conference 2018.

If you are a Gem-A Member or Student you will have received an email to book member or student rates, if you haven't received it please contact membership@gem-a.com.

Cover Image: Portrait of Herbert Smith, which hangs in the Herbert Smith Room at Gem-A HQ in London.


The Fascinating History of Antique Turquoise Jewellery

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

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

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

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

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

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

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

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 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

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


 

Additional Info

Read more...

Leading the World's First Gemstone Testing Laboratory: Gem-A's Basil Anderson

As we build up to the Gem-A Conference 2018 in November, we are continuing our celebration of the Gem-A Greats who have been pivotal in our history. This week’s Heritage Series turns to another of Gem-A’s founding fathers, Basil Anderson.

Basil Anderson with X-ray equipment. Image Credit Gem-A.

At a time when the gemmological world and the jewellery industry were rapidly changing with new innovations and the appearance of sophisticated synthetics, Basil Anderson was a pivotal figure in ensuring the link between gemmological science and industry-practice. His commitment to maintaining the important relationship between gemmologist and jeweller is still at the heart of Gem-A’s educational ethos to this day.

READ MORE: Heritage Series, Dr Herbert Smith 

Educated at Kings College London, Anderson graduated with a first class degree in Chemistry and Mineralogy in 1924. That same year he was introduced via his professors to Mr Tanburn of Hatton Garden, who was actively looking for someone to run the world’s first gemstone testing laboratory.


Original Notes from Anderson's colleague CJ Payne at the Testing Laboratory. Image Credit Gem-A

This was a critical time for the gemstone and pearl industry. With innovations such as Mikimoto’s development of cultured pearls in 1921, the jewellery industry was in a transitional period as it responded to the impact of synthetics on the industry.

In direct response to this new crisis, the London Chamber of Commerce created the ‘Diamond, Pearl and Precious Stone Trade Branch’ – with the aim of creating a laboratory to authenticate gemstones and pearls. The recently graduated Basil Anderson, much to his own humble surprise, was the ideal candidate, and in his 1981 lecture to Gem-A he recounted how he ‘toddled along’ to Hatton Garden for his interview. It is safe to say Anderson was successful, and following an all-important cup of tea, he began running the world’s first gemstone testing laboratory.

Collection of Anderson's Laboratory Notes from 1925. Image Credit ©Gem-A.

For Anderson, the jewellery sector was a “very ancient trade and it has always been a very honourable trade”, and the appearance of mass synthetics was “innocuous” because the chain of confidence – from miners to dealers to lapidaries to manufacturers to retailers – was shaken by the introduction of synthetics.

READ MORE: Birthstone Guide, Spinel for those born in August

So while Gem-A was created out of a need to provide gemmological education for the jewellery trade in 1908, the first gemstone testing laboratory was likewise created out of the need for gemmological knowledge and scientific authentication to safeguard integrity.


Original and latest editions of Anderson's Gem Testing.

Indeed, the very title of his 1942 book Gem Testing for Jewellers crystallises Gem-A’s ethos of providing gemmological knowledge to support jewellers, and of expanding gemmological science to reach jewellers, traders and the developing gemmological community. In the book’s original preface, Anderson stated it was intended “to reinforce the invaluable knowledge which the jeweller has gathered by virtue of long experience, to reinforce this knowledge by making it more conscious and giving it a firmer factual basis”.

READ MORE: Journal Digest, Rainbow Lattice Sunstone 


The Chelsea Filter, patented by Gem-A

LEGACY
Anderson ran the testing laboratory from 1924-79 and soon became the preeminent expert on pearl authentication of his day. While teaching Gem-A’s Gemmology Diploma, Anderson invented the Chelsea Colour Filter in 1934 with his colleague CJ Payne and the students at Chelsea Polytechnic, which is still sold today by Gem-A Instruments and used worldwide.

Early Advert for the Chelsea Colour Filter

Anderson became our head examiner 1951, succeeding Dr Herbert Smith, and was later voted in as Vice President in 1976.

READ MORE: Gem Empathy IJL Competition 2018

Anderson understood and advocated the importance of science and experience working together to the benefit of all in the gemmological and jewellery industry, so that traders were not hazarding opinions but could make informed factual analysis. Basil Anderson’s legacy to Gem-A can be seen in the laboratory named for him at Gem-A HQ in London, and in the annual awards in his honour at Gem-A graduation: the Anderson Medal, awarded for the best set of papers on the Foundation examination, and the Anderson/Bank prize for the best Gemmology Diploma theory paper. In 2013, Anderson was named in the French Association of Gemmology’s 50 most influential gemmologists of all time.


Basil Anderson, Image Credit Gem-A

As we look forward to the Gem-A Conference and Graduation this November, those graduates who are awarded the Anderson medals become a part of our proud history, together with our founders who helped to shape the gemmological world of today. 

If you would like to join us in celebrating 110 years of gemmology education click here and register for the Gem-A Conference 2018.

If you are a Gem-A Member or Student you will have received an email to book member or student rates, if you haven't received it please contact membership@gem-a.com.

Cover Image: Photographs of Basil Anderson in the Gem-A collection. Image Credit Gem-A


The Fascinating History of Antique Turquoise Jewellery

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

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

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

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

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

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

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

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 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

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


 

Additional Info

Read more...

Focus on Gemstone Fluorescence: Looking for the Light

Most of us know about fluorescence in gemstones, but how many use it as part of their gemmological testing routine? Here, Gem-A gemmology tutor Lily Faber, FGA DGA EG, delves deeper into fluorescence and explains why it can be both enlightening and enjoyable for gemmologists.

Luminescence in Gemmology

When we use the term luminescence in gemmology, it generally refers to the term photoluminescence, which is the emission of a cold, visible light when a gem material (or general substance) is excited by light of a shorter wavelength. Two examples are fluorescence and phosphorescence.

Fluorescence occurs when a gem material is illuminated by radiation of shorter wavelengths with higher energy.

A bag of cubic zirconia under LWUV with areas of blue fluorescence that highlights the presence of diamonds. 

The visible light emitted stops when the source of illumination is turned off. Phosphorescence, on the other hand, is a visible light that is emitted by a gem material after the original source of exciting radiation has been switched off.

The Hope Diamond Phosphorescence

A famous example of a gemstone that strongly phosphoresces is the blue Hope Diamond, which glows a bright red for several minutes after being excited by short wave UV light. Both fluorescence and phosphorescence can have varying strengths from very strong to weak. If a material does not either fluoresce or phosphoresce, it is considered inert.

Quartz under LWUV showing oil inclusions.

The History of Gemstone Fluorescence

Fluorescence has been observed for years, but it was not until Sir George Stokes extensively documented this effect in relation to gemmology that it officially became part of the scientific lexicon. In 1852, Sir George coined the word fluorescence, named after fluorspar, more commonly known as fluorite, which is a highly fluorescent material.

The ‘Stokes Law of Fluorescence’ or ‘Stokes Shift’ states that the fluorescent emission of light will always be that of a longer wavelength than the excitation source, i.e. the light emitted is of a lower energy than its excitation source.

Why Use Fluorescence to Test Gemstones?

Fluorescence can be a helpful tool when used correctly. Some gemstones have a characteristic or, very rarely, a diagnostic reaction to UV light. One gemstone that notably both fluoresces and phosphoresces is a diamond, which typically fluoresces blue in longwave UV light and then phosphoresces yellow.

This is a diagnostic result for a colourless to yellow diamond in the Cape series (Type Ia), but please be aware that fluorescence is rarely diagnostic as reactions may vary wildly within the same species or variety of gemstone.

READ MORE: The Fascinating History of Platinum

Fluorescence can indicate or confirm the identity of a stone. For example, citrine quartz is inert to fluorescence due to the presence of iron, which eliminates fluorescence. If you are testing a yellow stone that may potentially be a citrine, and it fluoresces orangey-yellow under LWUV and red under SWUV, it cannot be a citrine and is more likely to be a scapolite.


Scapolite from Ontario under LWUV.

Other reasons to use fluorescence? It is quick and normally takes less than one minute to observe reactions. You can test gemstones that are loose, set, rough or fashioned, and you can test either single gemstones or multiple gems at the same time. Finally, it is entertaining!

How Does Fluorescence Occur in Gemstones?

Ultraviolet light (UV) is the most commonly used excitation source. We cannot see UV light as it sits just below the visible light spectrum (400nm- 700nm) at 10-400nm. UV light enables us to see fluorescence because a gem material will absorb this radiation source and then emit light that is lower in energy and therefore visible to the eye. But what is actually happening within the gemstone itself to elicit such a colourful reaction?

It has to do with electrons. When electrons are excited by a source of radiation, they jump to a higher energy level around the nucleus of the atom. The excited electron remains in this excited state for a short period of time until it falls back to its original ground state. As the electron returns to its ground state, it emits energy either as heat or as visible light (fluorescence).


A: Natural spinel, red paste, synthetic verneuil ruby, almandine garnet and two natural rubies.
B: The same stones under LWUV. C: The results under SWUV.
 

If you are wondering if all minerals fluoresce, the answer is no. Only 15% of all known mineral species exhibit this effect, the causes of which can be very complex. One of the more better-known and documented causes is the presence of activator elements that can be excited by higher energy wavelengths.

Some activators include chromium (Cr), uranium (U), manganese (Mn), lead (Pb), titanium (Ti) and rare earth elements (REE). Some elements are considered to be the complete opposite, however, and when present they eliminate or quench fluorescence, causing a gemstone to be inert. Common quenchers include iron (Fe) and nickel (Ni).

 
Kunzite under SWUV.

Using UV Light to Test Gemstones

The types of UV light used in testing are long wave (LWUV) with a principle wavelength of 365nm, and short wave (SWUV) with a principle wavelength of 254nm. Different testing equipment ranges from UV keyrings (typically LWUV) to a UV viewing cabinet. When using UV light to test gemstones, it is important to remember that any exposure to UV light can damage your eyes, but particularly use caution when using SWUV as it is more dangerous than LWUV. Always wear protective UV goggles or ensure that your UV cabinet is installed with an eyepiece that filters out UV light.

To properly use a UV keyring, take the following steps:

  • Never look directly into the light
  • Turn off surrounding lights so you are in a dark environment.
  • Place the gemstone table-down if facetted. If table up, the gemstone may reflect the UV light into your eyes and creating confusing, conflicting or inconclusive results.
  • Hold the keyring approximately two inches away from the stone and, if testing multiple gems, always be consistent with the distance at which you hold the light.
  • Record whether the stone is inert or fluorescing, and the strength of the reaction.

Sometimes you may see some dull purple or red light in the gemstone or on a few facet edges. This means that the gemstone is reflecting the purple UV light and is not itself a fluorescent reaction.   


A: Synthetic verneuil sapphire, scapolite, natural sapphire, topaz and citrine. B: Under LWUV. C: Under SWUV 

Understanding Fluorescence Results

While fluorescence is not a diagnostic test, and results can vary dramatically even within the same gemstone species (variable emerald results, for example), it can be a useful indication of what a gemstone is. When testing diamonds and colourless, transparent simulants, keep the below chart in mind.

When testing red to pink gemstones,do keep in mind that natural rubies in particular may have variable fluorescence based on their iron content. If iron is present, the ruby will have minimal to no fluorescence. Synthetic rubies tend to have much stronger fluorescent reactions.

When testing green gemstones, fluorescence can be tricky to use for identification purposes. However, it may be useful in terms of recognising the presence of fillers in emeralds or green jadeite jade, for example.

Some resin fillers fluoresce a whitish colour under LWUV and if this reaction is seen in either of the aforementioned stones, it may be an indication that filler is present, especially if the fluorescence is concentrated in seams or certain areas rather than being evenly distributed across the stone.

Note the natural emerald fluorescing a whitish colour (second from right), hinting that a resin filler may have been used. Further testing will be needed to confirm this possibility.

Left to Right: synthetic flux emerald, synthetic hydrothermal emerald, natural emerald, chrome diopside.

Additionally, natural emeralds, if they do fluoresce, will have a red to inert reaction under LWUV, and a weaker inert or green reaction under SWUV. Synthetic emeralds may fluoresce red or, in the case of the synthetic hydrothermal emerald, they may be inert if doped with iron to imitate a natural inert reaction.

Untreated green jadeite does not fluoresce, so any other reaction should be regarded with suspicion and further testing will be needed. When testing yellow gemstones the bottom chart may prove useful.

Conclusion - Fluorescence in Gemstones

As is evident, fluorescence can be a helpful tool when testing gemstones, though not always diagnostic. It is a quick test that is one of the more exciting ones in the world of gemmology. ■

All images courtesy of Lily Faber and Gem-A gemmology tutor, Pat Daly.

Colourless Gemstones

LWUV

SWUV

Diamond (natural)

Strongest reaction, most common is blue, but can be yellow and green

Similar colours to LWUV but it is a weaker reaction

Diamond (synthetic)

Similar colours to SWUV but it is a weaker reaction

Strongest reaction, mainly fluoresce orange to yellow

Cubic zirconia

Yellow to dull-orange, variable

Weaker reaction to LWUV or inert, similar colours

Synthetic moissanite

Variable reactions

Variable reactions

Synthetic spinel

Inert

Bright, chalky white or blue/green

Paste

Inert

Variable, may have chalky white surface

 

Red and Pink Gemstones

LWUV

SWUV

Ruby (natural)

Variable, strong red to inert

Same as LWUV but weaker to inert reaction

Ruby (synthetic)

Bright red, tends to be stronger than natural ruby

Red, weaker than LWUV but still brighter than natural ruby

Red spinel

Red

Red, but weaker than LWUV

Spodumene, var. Kunzite

Orange or violet

Weaker violet, whitish or inert

Almandine garnet (Iron is present, this stone never fluoresces)

Inert

Inert

Red glass/paste

Inert

Variable, may have chalky white surface

 

Yellow Gemstones

LWUV

SWUV

Quartz, variety cirtrine

Inert

Inert

Yellow sapphire (natural)

Apricot orange to inert

Inert

Yellow sapphite (synthetic)

Weak red to inert

Inert

Yellow scapolite

Yellowish

Reddish

Yellow topaz

Yellowish

Whitish

This article originally appeared in Gems&Jewellery Summer 2018/ Volume 27/ No.2 

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: Willemite and calcite fluorescing under SWUV.


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Heritage Series: The Trailblazing Efforts of Robert Webster

Our Heritage Series celebrates some of the most prominent figures in Gem-A's History who have helped to shape the world of gemmology today. Listed in the French Association of Gemmology's '50 Most Influential Gemmologists of All-Time', this instalment turns to Gem-A's most prolific writer: Robert Webster.  

Born in 1899, the young Robert Webster left school at the age of 15 to support his widowed mother, and his father’s footsteps as a pawnbroker. As Basil Anderson notes in his touching obituary to Webster, this proved to be a valuable training ground for the practical gemmologist.


Webster and his Gemmology Class © Gem-A

During the First World War, Webster was awarded the Military Medal for his bravery in carrying messages under fire, and on returning to England he began studying gemmology at Chelsea Polytechnic under Mr I.G Jardine. It was here in 1933 that Webster met the recently appointed lecturer in gemmology, Basil Anderson, at a time when the gemmological world was, in Anderson’s own words, “advancing on all fronts”.

Webster soon became a regular contributor to The Gemmologist (predecessor to The Journal of Gemmology) specialising particularly in ivory, and he secured his Gemmology Diploma a year later in 1934.


Early Articles by Webster.

Robert Webster’s gemmological career went from strength to strength: in 1942 he became an assistant lecturer at Chelsea Polytechnic and, following WWII, he was invited by Basil Anderson to join the Testing Laboratory team in Hatton Garden, to tackle the new challenge of calibré synthetic corundum. In the first year alone they tested 105,000 stones!

In the 1940s the Gemmological Association established the Research Diploma, to encourage and recognise excellent postgraduate research by Fellows of the Association. Robert Webster is one of only six people to be awarded this coveted Diploma for his thesis on ivory and its various imitations. It made such an impact that renowned mineralogist Dr Herbert Smith added sixteen pages to his 1949 revision of Gemstones!

Collection of Editions of Webster's Compendium, with document from Annual Report of the testing lab for the London Chamber of Commerce

In 1937 Webster published his Gemmologists’ Pocket Compendium with “the intention to cover as concisely as possible all the information most useful to the practical gemmologist”. This captured the spirit of Gem-A’s ethos since 1908 of providing quality gemmological education for the benefit of the gems and jewellery industry, and was built on the very data recorded by Basil Anderson and C.J Payne, the compendium has been the ‘bible’ of professional and amateur gemmologists and retail jewellers.

Together with his 1941 Practical Gemmology and epic two-volumed Gems in 1962, Webster’s contribution to gemmological research has made him one of the most recognised voices in Gem-A history. His prolific work is still held in high esteem, to such an extent that when contributors were invited to revise Gems, gemmologists from Australia, Canada, Germany, Thailand, Vietnam, the UK and the USA answered the call.

Robert Webster © Gem-A.

On Webster’s death at the age of 77 in 1976, Anderson’s touching tribute to his friend’s memory serves as a testament to Webster’s impact on the gemmological world:

"So manifold and varied were the activities of Robert Webster in the field of gemmology that the gap left in our ranks by this death can never adequately be filled – not, at least, by any one person."

Robert Webster is remembered at Gem-A as one of our greatest gemmologists. Future gemmologists studying at Gem-A HQ in London are taught in the Webster Room, dedicated to his memory. To this day, Webster’s Gemmologists’ Compendium remains one of the most comprehensive guides for anyone studying gemmology. 

If you would like to join us in celebrating 110 years of gemmology education click here and register for the Gem-A Conference 2018.

If you are a Gem-A Member or Student you will have received an email to book member or student rates, if you haven't received it please contact membership@gem-a.com.

Cover Image: Photograph of Robert Webster from the Gem-A collection. Image Credit Gem-A


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