If you have had the chance to visit us here at Gem-A HQ, you may have had the opportunity to see the Sir James Walton Library, which is one of the largest collection of gemmological books in Europe and holds some of the greatest works in gemmological science, including Walton’s Practical Gemmology. But did you know that for the majority of his life Walton was a decorated medical professional and a surgeon to royalty?  

Sir James Walton was the President of the National Association of Goldsmiths 1953-55 and served as the Gemmological Association’s Chairman in 1955, following a long illustrious medical career. Walton was awarded the Fellowship of the Royal Colleges of Surgeons among his many qualifications, and was established both as an Officier de la Legion d’Honneur, and a Knight Commander of the Royal Victorian Order (K.C.V.O) which recognises personal service to a reigning monarch of the United Kingdom.

Sir James Walton

READ MORE: Heritage Series: The Trailblazing Efforts of Robert Webster

Born in 1881, James Walton was elected to the staff of the London Hospital in 1913, where he worked for 33 years. During the First World War, Walton was a Captain in the Royal Army Medical Corps (RAMC). Walton was stationed at the 2^nd London General Hospital and served as a surgeon to the Empire Hospital specialising in diseases of the brain and spinal cord, and in WWII he was a Brigadier in the Army Medical Department.

In 1930, Walton was also appointed as surgeon to the Royal Household of King George V, and served through both his reign and those of his sons Edward VIII and George VI, until 1949. During his dedicated service he was official surgeon to Queen Mary from 1936-49, and it was through their shared enthusiasm for gemmology that Queen Mary honoured the Association by visiting the Gemmological Association’s Exhibition in 1951 at Goldsmiths’ Hall.

Queen Mary, Sir James Walton, and President Dr Herbert Smith
at the 1951 Gemmological Association Exhibition

Dedication in Walton's Practical Gemmology

READ MORE: Speaker in the Spotlight: Q&A with Dr Eloïse Gaillou

After an illustrious career, serving as President of the Association of Surgeons and the Medical Society of London respectively, Walton began his well-earned retirement in 1946, where he entered the fascinating world of gemmology.

While his investigation of gemstones was an enjoyable hobby, by Walton’s very nature this hobby developed into an intensive and specialised study. Despite not having the traditional background of most gemmologists, Walton mastered the subject of Crystallography and became a recognised authority on precious stones in the UK, accumulating in his book Practical Gemmology.

Dedications to B.W. Anderson and to Dr Herbert Smith by Sir James Walton in his 'Practical Gemmology'

Described by Robert Webster as ‘a valuable contribution to gemmology’ (JoG 1953 Vol.4.No.1), Walton’s book addressed an important gap: he had noticed that there was not a book aimed at the new or amateur gemmologist who did not have (or necessarily need) a scientific or geological background:

‘The majority of books are written in technical language and are interspersed with many mathematical proofs and equations from which they [non-specialists/hobbyists] shrink with aversion if not with horror.’

Walton aimed to gather ‘an account of the scientific principles upon which the subject of mineralogy is based’ but to ‘divest it as far as possible of all mathematical considerations, to present it in the simplest non-technical language…so that it may be of easy understanding even to those devoid of all scientific knowledge.’

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

That being said, Walton’s book is of incredible scientific value, and included unpublished material by Basil Anderson and CJ Payne, who supported this important project that created an essential book for those who approached gemmology out of inquisitive enthusiasm. In 1947 Walton was also appointed the first curator of the Association’s collection of gemstones.  

Sir James Walton

Upon his death in 1955, a vast collection of Sir James Walton’s books and stones were generously bequeathed to the Association, and are now housed in the Sir James Walton library at Gem-A HQ London. So when you next visit us at Ely Place, please ask to visit our exquisite library and immerse yourself in a part of Gem-A history and Walton’s living legacy.

The Sir James Walton Library at Gem-A HQ London

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 Sir James Walton from the Gem-A collection. All Image Credits: Gem-A.

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The Fascinating History of Antique Turquoise Jewellery

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

Read more

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Birthstone Guide: Garnet For Those Born In January

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

Read more

---

Getting Started with Quartz Inclusions

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

Read more

---

Understanding Iridescence: Opals, Pearls, Moonstones and Fractured Stones

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

Read more

---

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

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

Read more

---

Tanzanite: The Contemporary December Birthstone

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

Read more

---

Birthstone Guide: Turquoise For Those Born In December

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

Read more

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Understanding the Cat's Eye Effect in Gemstones

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

Read more

---

Jade and its Importance in China

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

Read more

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Highlights of Gem-A Conference 2019

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

Read more

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The captivating opal is the birthstone for all those born in October. Here, Gem-A tutor Lily Faber FGA DGA EG explores the history and properties of this iridescent and rainbow coloured gemstone.

Opals have been valued for millennia, even before Ancient Greek and Roman times. There are two main types of opal: precious and common. The precious variety shows the magical play-of-colour that is so highly sought-after, while the more common variety simply does not show this optical effect but can come in a variety of colours from pink to green to blue to yellow.

Read more: Understanding the Different Types of Opal

Common Opal from Ethiopia, Image Credit Pat Daly.

Another variety is known as fire opal, which is a transparent to translucent variety that is orange, red or yellow and sometimes displays play-of-colour, but often does not.

The History of Opals

Believed by the Greeks to give one the power of prophecy and foresight, opals enjoyed a long period of favour. The Romans thought that opals represented purity and hope and they were regarded in high esteem until the 18th and 19th centuries when perceptions changed.

In the Victorian era especially, opals were believed to be unlucky and a cause of misfortune. Some even went as far as to believe that opals could bring physical harm to their wearer.

Read more: How to Assess the Value of an Opal

A well-known example of this is Queen Alexandra, a successor to Queen Victoria. She inherited a spectacular tiara that Prince Albert gifted Queen Victoria containing 11 precious opals. Fearing the opals could bring her misfortune, Queen Alexandra swiftly replaced all the opals with rubies before continuing to wear the heirloom.

Opal with Striated Colour Patches. Image Credit: Pat Daly.

Where are Opals Found?

Prized precious opals were relatively rare prior to the 19th century, the best examples coming from present-day Slovakia. Today, there are many localities where opals can be found, but the best and most valuable ones were discovered in the late 19th century in Australia.

Deposits where highly desirable opals have been found include Lightning Ridge and White Cliffs in New South Wales.

Understanding Synthetic Opals

There are many natural opals on the market, but there are also manmade ‘synthetic’ opals. First created by Pierre Gilson in 1974, these opals are very close to matching the physical and chemical structure of a natural opal. Synthetic is in quotations because it is not completely identical to its natural counterpart.

Synthetic Opal - Columnar Structure. Image Credit, Gem-A, Pat Daly.

It is essential that one must be able to distinguish between these manmade opals and the naturally forming ones when going to purchase an opal. This can be done with observation using a 10x loupe.

Natural opals with play-of-colour have irregular patches of rainbow hues that flash at many different levels within the stone as it is turned. The patches of colour are irregularly shaped and can be limited depending on the inner structure of the opal.

Identifying Synthetic Opals

‘Synthetic’ Gilson opals still display play-of-colour, but it can be much brighter and more consistently shaped and displayed throughout the stone than natural opals. Additionally, these patches of colour have a polygonal outline to them, giving a ‘lizard skin’ appearance.

If cut as a cabochon, there will also be a columnar structure to the patches of colour on the side of the cabochon, which is completely unlike natural opals.

Boulder opal. Image Credit: Gem-A.

Caring for Opals

Opals contain up to 30% water, which means that they are susceptible to drying out when exposed to heat. This can cause crazing, or cracking, that is irreversible.

When storing your opals, always make sure that it is in a cooler temperature, preferably with a bit of moisture in the air (a small dish of water or cotton ball will do). Opals are also porous and can be easily damaged by acids and chemicals such as detergents, perfumes and jewellery cleaner.

An example of crazing on a white opal. Image Credit, Gem-A, Pat Daly.

Finally, opals are soft with a hardness of 6 on the Mohs scale. This makes them vulnerable to knocks, scuffs and abrasions, which means they are more suited for earring and necklace settings rather than rings in order to keep them safe while wearing.

Today, opals are enjoying resurgence in popularity, despite the misgivings that they can bring back luck to those who wear them. For those born in October, opals can and should be considered a bit of gemstone magic to be enjoyed for their stunning play-of-colour unmatched by any other gemstone.

Start your gemmology journey with bite-sized Short Courses and Workshops.

Would you like to learn more about the science of gemmology? Discover our gemmology courses here. 

Cover image: Precious Opal Matrix. Image Credit: Pat Daly. 

Did you know that two of Gem-A’s presidents were actually Nobel Prize Winners? Sir William Henry Bragg, the Association’s president 1937-42, and his son Sir Lawrence Bragg president 1954-72, were jointly awarded the Nobel Prize for Physics in 1915 for their research in X-ray Crystallography – an epic achievement that laid the foundation for future scientific breakthroughs and the basis of 26 other Nobel Prize winners and counting!

William Henry Bragg (WHB) had an exceptional mind, winning a Minor Scholarship to Trinity College, Cambridge, at the age of 17! The family considered this a bit too young, so a year later in 1881 WHB began the Mathematical Tripos at Trinity, and after graduating he began research at Cambridge’s Cavendish Laboratory to train in physics.

Sir William Henry Bragg. Image Credit: Gem-A.

In 1886, at the age of 23, he was appointed the Elder Professor of Mathematics and Experimental Physics at the University of Adelaide. Much of his time was taken with teaching commitments, leaving little room for research, but WHB maintained his interest in physics and kept up to speed with the latest developments by Prof. Wilhelm Röntgen at Würzburg, Germany, who had discovered an exciting new form of radiation, ‘so mysterious that he called it the X-ray’ (Hunter 2004: 6-8). At 41, WHB began to explore X-ray radiation, winning international recognition and was nominated to the Royal Society in 1907, and took the Cavendish Chair in Physics at Leeds, England in 1909.

Bragg’s first son, William Lawrence (WLB), was born in 1890 and later recalled that his father would tell his sons bedtime stories about the properties of atoms “We started with hydrogen and ran through a good part of the periodic table.” (Hunter 2004: 8; RI, MS WLB pp8-12).  Equally brilliant, WLB entered the University of Adelaide a year early at the age of 15 and achieved a First Class Hons in mathematics. When the family moved to England, WLB, like his father before him, entered Trinity College Cambridge, but switched from mathematics to physics.

Sir William Lawrence Bragg.
Image Courtesy of the Royal Institution of Great Britain.

WHB was aware of the recent Munich Experiment of 1912 where Max von Laue, Walter Friedrich and Paul Knipping targeted sphalerite crystals with X-ray beams, backed with a photographic plate to track the diffraction pattern. Today, gemmologists are quite familiar with diffraction patterns from X-ray spectroscopy, however, it is important to remember that at this time, scientists were still establishing the nature of X-rays, whether we were talking about waves or atom particles, and WHB was still yet to invent the first X-ray spectrometer:

"Nothing was certain then, X-rays were mysterious"
 Prof. André Authier, Université Piérre et Marie Curie.

It was the 22 year old WLB who fully realised the ramifications of Laue’s epic discovery that X-rays were diffracted by the crystal structure: he established the relationship between the wavelength of radiation, angles of incidence and diffraction, and the spacing of layers of atoms in a crystal structure. Knowing the first two, the third could be calculated. This became known as Bragg’s Law:

n λ = 2d sin θ

d being the distance between atoms by using geometry

This leap of genius was the key to measuring and understanding atomic structures, which could only be inferred up to that time. As he later said in his 1959 lecture to the Royal Institution:

"What is it, really, that makes a thing a crystal? It is it’s inside arrangement, it’s the fact that the molecules or atoms in it are an absolutely regular pattern, like soldiers on parade."

Crystallography in the Sir James Walton Library at Gem-A HQ. 

To facilitate this his father WHB designed the X-ray spectrometer:
"It contained a platform on which the crystal could be rotated with respect to the X-ray beam and an ionisation chamber that could be rotated around the crystal. The ionisation chamber contained a gas that was ionised by X-rays and an electrometer so that the amount of radiation detected could be qualified." (Hunter 2004: 35)

The impact of the Braggs’ research – and Bragg’s Law – cannot be overemphasised:

"it could be well argued that the scientific method of X-ray crystallography has been as great as those of quantum theory and relativity, and the impact on everyday life even greater." (Hunter 2004: xiii)

From this exciting realisation, father and son worked tirelessly over the Summers of 1913 and 1914, and in 1915 the younger Bragg received a telegram whilst on the Front in the First World War that he and his father had been awarded the Nobel Prize in Physics for their research in X-ray Crystallography.

This enshrined the Braggs into history.  Moreover, WLB was instrumental in supporting the British Expeditionary Force in France and Belgium in WWI by applying scientific sound ranging to locate enemy guns by sound.  In 1941 Bragg was a scientific liaison officer between Great Britain and Canada, and an advisor to the British Navy on antisubmarine work, and sat on the advisory council to the Minister of Supply.

Publications in the Sir James Walton Library at Gem-A HQ. 

Over the course of their careers both father and son were heavily involved with the scientific community at the Manchester Laboratory, the Cavendish Laboratory, and the Davy-Faraday Laboratory at the Royal Institution of Great Britain. Indeed, both Braggs were in turn appointed Resident Professor at the Royal Institution, and both served as Presidents of the Gemmological Association – a link that is revived again this year when we return to the Royal Institution for our Graduation, 80 years since William Henry Bragg presented awards to our graduates.

In his inaugural address WHB noted his honour at being our President:

Your Association has paid me a great honour in asking me to be your President…you must allow me to begin by address this evening by expressing my warm appreciation… I have of course no inner knowledge of your ancient, beautiful and wonderful craft and feel flattered that you have invited me, a physicist, whose concern in precious stones differs so much from that of the craftsman, to be associated with you in this honourable way… If, apart from their use as precious stones, crystals were regarded at one time as mere curiosities, the situation is entirely changed. We have learnt that the crystalline structure is one of the great orders of Nature, occurring everywhere and not merely in the rare specimen… I suppose that the jeweller looks to the diamond as the king of gems. To the physicist, the internal structure of the diamond is of extraordinary interest for its strong and beautiful simplicity and for the information which it gives as to the properties of the carbon atom. For the diamond consists of carbon alone, and the bonding facilities of the carbon atom are directly exhibited.  

Indeed, in keeping with the Basil Anderson's gemstone testing laboratory, WHB noted the importance of X-ray crystallography to the gemmologist, as it "gives you a means, if you need it, of deciding between the true and the false."

In 1954, Sir Lawrence Bragg was extended the same invitation to become our President. In his address, WLB appreciated the honour as both his father and their close friend, Sir Henry Miers, had both served the Association in this way. Just as we were created as a means to provide gemmological education to the wider jewellery industry, WLB firmly believed that scientists had a duty to share their knowledge:

"There is one sense, however, in which the pure scientist is, in my opinion, deeply wrong in withdrawing into his ivory castle.
He must pursue knowledge for its own sake,but at the same time it is his duty to see that
this knowledge is so digested, arranged, and simplified that it can become a possession of all those who desire to attain it."

It is fitting, then, that in 2018 we will be celebrating our Gemmology Diploma and Diamond Diploma Graduates at the Royal Institution on November 5, celebrating 110 years of creating gemmologists worldwide.

The Royal Institution of Great Britain. Image Credit: SB Gem-A.

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 Lawrence Bragg, Courtesy of the Royal Institution of Great Britain. 

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The Fascinating History of Antique Turquoise Jewellery

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

Read more

---

Birthstone Guide: Garnet For Those Born In January

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

Read more

---

Getting Started with Quartz Inclusions

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

Read more

---

Understanding Iridescence: Opals, Pearls, Moonstones and Fractured Stones

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

Read more

---

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

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

Read more

---

Tanzanite: The Contemporary December Birthstone

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

Read more

---

Birthstone Guide: Turquoise For Those Born In December

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

Read more

---

Understanding the Cat's Eye Effect in Gemstones

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

Read more

---

Jade and its Importance in China

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

Read more

---

Highlights of Gem-A Conference 2019

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

Read more

---

From the Summer 2018 issue of Gems&Jewellery, Gagan Choudhary FGA, deputy director of Gem Testing Laboratory Jaipur, describes the various types of fake gem rough that has passed his desk in recent months, including mica rock presented as emerald rough, cubic zircona and topaz fashioned as diamond octahedtrons, and synthetic quartz mimicking aquamarine.

Reaching directly to the miners for procuring rough has always been profitable, but involves a huge amount of risk unless one has enough experience in buying at the source, deep knowledge about the stone being purchased, and handling the pressure thereof.

Often, there have been cases when dealers tend to forget the possibilities of scams and frauds at mining sites or the markets nearby. The sellers at such locations often present glass, synthetics, treated gems or other cheap natural materials as expensive gems in order to make some quick money. This practice has been prevalent at most of the major mining regions around the world for decades.

At Gem Testing Laboratory Jaipur, we routinely encounter such cases, some of which are presented here:

GLASS-FILLED MICA-ROCK, PRESENTED AS EMERALD ROUGH

Recently, a 1,075 gm black micaceous rock was presented for identification (1), a true example of a fraudulent rough, which, although not shocking to us, was definitely an interesting one. Initial observations with unaided eyes from different angles suggested the presence of several crystals, with hexagonal profile, embedded in the rock.

Such rock formation is a common sight for those dealing in emerald rough, especially from locations where emerald is associated with mica (phlogopite) schist, such as Zambia. Careful observation using strong fibre-optic light surprised us. Under reflected light, only small areas or corners of the embedded crystals appeared green.

The rest appeared dark, due to the presence of black mica on and around crystals.

1: This 1075 gm micaceous rock was embedded with elongated ‘hexagonal’ crystals of artificial glass (marked with arrows).
Note the difference of texture around embedded crystals and rest of the rock.

However, when light was transmitted through these crystals, they appeared bright green, which raised suspicion about their origin. Such bright green colour under transmitted light, especially in an embedded crystal, had never been seen before. Further examination revealed a granular texture around these embedded crystals, while the rest of the rock appeared flaky; this supported our suspicion.

These features suggested that micaceous rock was first drilled, filled with green ‘hexagonal’ crystals artificially, and then the joints were covered with a mixture of glue and black mica.

When observed under ultraviolet light,  corners of the embedded crystals (micafree areas) fluoresced chalky-yellow green. Raman analysis confirmed these embedded crystals as artificial glass. 

MICA-COATED GLASS IMITATING EMERALD ROUGH

Another form of emerald-rough imitation are these mica-coated glass (2). In this case, pieces of green glass are first fashioned in the shape of hexagonal rough, which is then coated with fine powder of black mica mixed in glue, followed by a layer of mica chips. These worked-up pieces are then taken to the mining sites by the middlemen and mixed in parcels of low-quality natural emeralds.

The illustrated glass specimens here were seen in a parcel of emeralds from Jharkhand, India.

 2. Glass samples worked-up to imitate emerald rough by fashioning into hexagonal crystals and coating with black mica.
Found mixed in a  parcel of natural emerald. 

SYNTHETIC RUBY FROM MOZAMBIQUE

We came across a small parcel of rough rubies (five pieces, weight range of 3.60- 18.06 ct) submitted for identification. All the specimens were tumbled with a corroded surface and interestingly coated with a yellow-brown substance. Most of the samples were free from inclusions, but under immersion microscopy all displayed curved growth lines, characteristic of synthetic ruby grown by Verneuil process (3).

Appearance of these specimens clearly suggested that they were presented as natural. Prior to this we have seen many more specimens of synthetic ruby, and in much larger sizes, presented as natural. As per the discussion and information from the depositor, these stones were purchased in Mozambique.

3. Rough Samples weighing 3.60-18.06 ct were identified as synthetic ruby. 
note the presence of yellow-brown substance on the extreme right, imitating mud on natural rough

NATURAL AND SYNTHETIC RUBY COMPOSITE

This 28.73 ct bright red rough, associated with some black and white minerals, was presented as a natural ruby. Upon initial examination with unaided eyes, the surface displayed some areas of milky angular zones against a pinkish to purplish background, typically seen in natural ruby crystals.

When examined under transmitted light, a large central area of the specimen appeared bright red, while the edges appeared dark and opaque (4). This raised suspicion about the origin of this rough.

Careful examination under the microscope revealed a sudden change. of growth and inclusion patterns, not only in the core and surface, but also within the surface; the surface displayed small chips with different inclusion patterns.

In addition, distinct colour variation between the core and edges of the specimen was evident. These features suggested that the specimen is a composite where a transparent piece of synthetic ruby is covered with small chips of natural ruby.

4.This bright purplish red-pink rough(top) is a composite of synthetic and natural ruby. The central part is a synthetic ruby while the out part is composed of chips of natural ruby.
Under transmitted light (bottom) the central synthetic part of the specimen appeared bright red, while the edges appeared dark and opaque.

SYNTHETIC SAPPHIRE, PRESENTED AS NATURAL ROUGH

Synthetic counterpart is a common imitation for natural sapphire rough; these are presented in two forms — one as broken, tumbled rough, and second, as fashioned, well-formed hexagonal-pyramidal crystals with surface markings (cover image). Although, their identification is not challenging in a gem lab, they might pose problems while buying at the mines.

The specimen illustrated in (5) was found mixed in a parcel of sapphires, purchased in Madagascar.

5. These two crystals, weighing 63.93 (left) and 44.66 (right) ct displaying bipyramidal habits and associated white mineral, were submitted as sapphire.
The crystal on left was identified as sapphire, but one on the right as glass.

GLASS AS SAPPHIRE ROUGH

Two blue crystals weighing 63.93 and 44.66 ct, as illustrated in were submitted together. Both crystals displayed bi-pyramidal habits and associated white mineral, typically seen in corundum. Interestingly, there was an obvious difference in colour and transparency of both the crystals; the crystal on the right had much better colour and transparency.

Closer inspection of the bright blue crystal revealed hemispherical cavities on its surface, coloured swirls and numerous gas bubbles — the features associated with glass. The grey-blue crystal (5, left) was proved to be natural sapphire, while crystal habit and associated white mineral (kaolinite) suggested Kashmir as its origin.

CUBIC ZIRCONIA AND TOPAZ AS DIAMOND OCTAHEDRON

Cubic zirconia as diamond imitation, both rough as well as cut, have been in existence for a long time, however, in recent years colourless topaz has become a frequent encounter in diamond imitation, especially in rough form. Image 6 illustrates one such example, where the left specimen is a cubic zirconia while the right one is topaz.

6. Cubic Zirconia (left) topaz (right).

These stones are fashioned as typical crystal forms associated with diamond, here, octahedron; often striations, grooves or triangular markings are created on these fashioned octahedrons, giving them a natural appearing crystal.

In the recent past, this author has encountered some large packets of such created ‘topaz octahedrons’, being presented as diamond.

Separation of cubic zirconia from diamond was easily done on the basis of higher specific gravity, while topaz by its anisotropic optic character. Although identification of these imitations is straightforward, when buying at mines or open markets one has to be careful. 

TREATED QUARTZ AS EMERALD ROUGH

In addition to the glass discussed above, emerald rough is often imitated by coated (7) or dyed quartz.

There have been cases where transparent quartz is painted with green colour and presented as emerald, however, as illustrated in 7 (left), such materials can be separated by crystal form (prism and rhombohedral faces) and horizontal direction of grooves or striations on prism faces.

Another material is the quartzite variety, which is first dyed green, then fashioned as hexagonal crystal shape to imitate emerald; such fashioned crystals are often coated with black mica too.

Even body colour, translucency and absorption spectrum (band at 650 nm) can separate such dyed materials from natural emerald.

 
7. Quartz crystals painted with green colour and coated with black mica are presented as emerald rough.
Also note the horizontal direction of grooves or striations on prism face.

SYNTHETIC QUARTZ AS AQUAMARINE CRYSTAL

This is one of the most unusual materials this author has seen for making a fake crystal — synthetic blue quartz fashioned as an hexagonal crystal of aquamarine (8). The crystal was fashioned into six-sided prisms, with pyramids and basal pinacoids — a crystal form commonly seen in aquamarine.

The crystal also contained a conical-tube with brown epigenetic material (such as iron oxide filling) visible to the unaided eyes. On observing the crystal from different sides, it displayed two parallel planes (seed plate) with colourless area and an attached metal clamp. Such features are often seen in synthetic quartz and other gems grown by hydrothermal process.

When viewed from the top i.e. down the ‘c’ axis, the interfacial angles between the prism faces ruled out the possibility of natural crystal form associated with crystals belonging to hexagonal crystal system, such as beryl.

As per the precision at which the nature operates, opposite sides of prism faces are parallel to each other, while in this case no opposite sides were parallel. Identification of this specimen as synthetic quartz was established on the basis of ‘bull’s eye’ optic figure, seed plate and infra-red spectra.

Such cases remind us of the importance of studying crystallography, not only for the identification of gem rough, but also in the creation of fake rough, which the maker of this fake missed out on.

8. Left: blue specimen presented as aquamarine was a synthetic quartz fashioned into a hexagonal crystal, terminated by pyramidal and pinacoidal faces. Also note the conical tube containing brown epigenetic substance. 
Right: the top view of the synthetic quartz specimen

CONCLUSIONS

Fake rough is an inevitable part of the gem trade, and the scams associated with this are increasing day-by-day. Identification of rough, especially in the field is quite challenging, however, one needs to keep in mind the existence of fake material in local markets or even mines.

Careful inspection of the presented rough before making a buying decision is always advisable, keeping in mind the crystallographic features. ■

All images courtesy of the author.

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: Synthetics presented as natural rough tumbled sapphire. Image Credit: Gagan Choudhary. 

---

The Fascinating History of Antique Turquoise Jewellery

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

Read more

---

Birthstone Guide: Garnet For Those Born In January

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

Read more

---

Getting Started with Quartz Inclusions

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

Read more

---

Understanding Iridescence: Opals, Pearls, Moonstones and Fractured Stones

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

Read more

---

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

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

Read more

---

Tanzanite: The Contemporary December Birthstone

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

Read more

---

Birthstone Guide: Turquoise For Those Born In December

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

Read more

---

Understanding the Cat's Eye Effect in Gemstones

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

Read more

---

Jade and its Importance in China

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

Read more

---

Highlights of Gem-A Conference 2019

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

Read more

---

There is one name in gemmological science that is synonymous with the study of Diamonds: BRUTON. Studying under the genius of Basil Anderson and Robert Webster, Eric Bruton had such an impact on the gemmological world that his work forms the basis of Gem-A’s Diamond Diploma to this day.

Born in London in 1915, Bruton started a career in publishing before joining the engineering branch of the RAF during World War II, where he was in charge of technical training and also served in India.

Eric Bruton ©Gem-A

On returning to the UK, Bruton was invited to edit four prominent publications: Industrial Diamond Review, Horological Journal, Goldsmiths’ Journal and – importantly for Gem-A – The Gemmologist, published by the National Association of Goldsmiths (NAG). Bruton immediately signed up for classes at Chelsea Polytechnic – then being led by Anderson and Webster – and began what would become a life-changing adventure into the world of gemmology.

READ MORE: Speaker in the Spotlight, Peter Lyckberg

Eric Bruton was awarded his Gemmology Diploma in 1950, and began teaching for the Association in 1967 – specialising in diamonds, running courses at St John Cass College London, and a similar course at Barcelona University – with examinations by The Gemmological Association of Great Britain. All of this was building up to Bruton’s breakthrough publication, his first practical handbook in 1970: Diamonds.

Until Diamonds, books on this subject were either highly technical or focused on one particular aspect of the industry. Recognising this problem, Bruton’s response was to cover all aspects of gem diamonds, spanning the history of diamond, mining and recovery, cutting methods, grading and valuation, and the identification of diamond and its simulants.

READ MORE: Investigating Fake Rough 

Throughout his research and his travels to various diamond mines across the world, Bruton realised that the various compartments of the diamond industry had little – or indeed no – knowledge of their counterparts. Most important of all, members of the public did not ‘appreciate that the possession of a diamond…has taken 4000 years of endeavour – blood, toil, sweat and tears – to produce the modern brilliant-cut diamond’ (viii).

Bruton was the ideal person to address this – with his editorial experience and gemmological expertise, he was in a rare and strong position to deliver.

Eric Bruton by David Langdon, 1971. Image Credit: Gem-A. 

Bruton’s Diamonds is a systematic study of all aspects of diamonds and forms the foundation of Gem-A’s Diamond Diploma. For many years, Bruton specialised in writing on all matters relating to gems, jewellery, and watches – and  even crime fiction! Bruton also founded the trade’s only newspaper of the time – Retail Jeweller – which, in competition with Watchmaker Jeweller & Silversmith - became the voice of the trade, and in 1994 was elected president of the Association.

READ MORE: Heritage Series, Let's Bragg About It! 

Today, Bruton’s contribution to the Gem-A is remembered with the Bruton Medal, a prize awarded to exceptional students with the best results in the Diamond Diploma examination, and the Bruton Room at Gem-A HQ in London, where future gemmologists study diamonds.

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 Trigons, photo by Pat Daly, with Bruton Medal. Image by Gem-A. 

---

The Fascinating History of Antique Turquoise Jewellery

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

Read more

---

Birthstone Guide: Garnet For Those Born In January

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

Read more

---

Getting Started with Quartz Inclusions

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

Read more

---

Understanding Iridescence: Opals, Pearls, Moonstones and Fractured Stones

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

Read more

---

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

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

Read more

---

Tanzanite: The Contemporary December Birthstone

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

Read more

---

Birthstone Guide: Turquoise For Those Born In December

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

Read more

---

Understanding the Cat's Eye Effect in Gemstones

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

Read more

---

Jade and its Importance in China

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

Read more

---

Highlights of Gem-A Conference 2019

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

Read more

---

As we enter the dark winter months, November’s birthstone citrine offers rays of warm yellow-orange sunshine. Here, gemmology tutor Lily Faber FGA DGA EG explores the properties and folklore around this sunny gemstone.

Citrine is a type of crystalline quartz that comes in many different hues of yellow, from pale buttercup shades to a stronger orangey or even brown-tinged yellow. Prized for its sunny appearance, citrine has long been popular in the gem and jewellery trade, especially in statement cocktail jewellery.

Citrine Myths and Folklore

For centuries, citrine has been said to hold the power of the sun. The stone is also believed by many to counteract depression and fight back against phobias. Citrine is known as a gemstone that can help its wearer remain calm in stressful situations because of its ability to attract good and positivity. Its characteristic yellow-to-orange colour is caused by a trace of iron in its structure.

Citrine Localities

Did you know? A little-known fact is that lots of citrine offered on the market is often amethyst that has been heat-treated to promote a golden colour. Natural citrine can be difficult to find, despite quartz being one of the most abundant gem minerals in the Earth’s crust.

Part of a citrine crystal. Photography by Henry Mesa, Gem-A. 

This gemstone is found worldwide, but some of the most important localities of note are Brazil, India, Madagascar and Sri Lanka. In Bolivia, amethyst and citrine hues can occur together in the same crystal. These multi-colour gemstones are called ametrine.

Citrine Crystals and Inclusions

Citrine can be found as stand-alone crystals or as a geode containing multiple crystals within a rocky pocket. If sold as an individual crystal, citrine will have a hexagonally shaped prism with a pyramidal termination and slightly thicker base.

Read more: Exploring the Varieties of Quartz

There may be fractures within the crystal that cause iridescence, and the surface may feature striations that run horizontally across the prism faces (if the surfaces have not been polished).

A heated Brazilian citrine of 128.78 carats in a StarBrite cut by John Dyer & Co. Photo courtesy of Priscilla Dyer. 

Inclusions in citrine can be highly variable. However, it mostly has similar inclusions to those in amethyst, such as tiger stripes, straight colour-zoning, incipient fractures (mentioned above), crystals and two-phase inclusions consisting of a liquid and a gas, or a solid crystal and a liquid.

Citrine Care and Caution

Quartz is a 7 on the Mohs scale of hardness, endowing it with the ability to be set into any piece of jewellery, whether it is a ring, necklace or earrings. Considered hard, citrine will resist scratches and abrasions, but it is not impervious to these attacks and care should still be taken when wearing it in everyday life.

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

Whether you like its appearance or the meanings behind it, citrine is a fantastic gem that can hold a high polish. This warm, bright and occasionaly overlooked gemstone that can be transformed into stunning pieces that add a touch of sunshine to any jewellery collection.

Read more: What Career Paths Can Trained Gemmologists Take? 

Start your gemmology journey by exploring our Short Courses and Workshops.

Discover more about the history of Gem-A and what makes our world-renowned gemmology education so special, here. 

Cover image: A rough citrine cyrstal specimen in the Gem-A Gemstone & Mineral Collection, photographed by Henry Mesa. 

From the Summer 2018 issue of Gems&Jewellery, Gem-A Associate Member and co-owner of Moriarty's Gem Arts, Steve Moriarty, shares his fascinating career in gemmology.

Although a gem specialist’s career can often start confined to a classroom or a lab, pouring over stone samples and peering through a microscope, our industry also offers wonderful opportunities to travel around the globe.

Steve Moriarty is not only the co-owner of Moriarty’s Gem Art in Crown Point, Indiana, but also an experienced gem-cutter and gem explorer. His family-run business, including the websitesmoregems.com, tanzanitejewelrydesigns.com, opallust.com and mothersfamilyrings.com, was founded in 1975, and today Steve, his wife Nancy, and two of their three children work together to offer a gem-orientated retail experience. Add to this Steve’s 25-years as a professional gem-cutter and it is clear that he has seen, worked with and sold some incredible gemstones.

READ MORE: Journal Digest, Blue Zircon

“Ever since I was young, I collected rocks and fossils,” Moriarty comments. “I really got interested in the gem business while I was in college; my brother Tom started importing gems from India and would send me stones, which I took to the jewellery arts classes to sell.”

Despite a stint as a chemist, Moriarty opted to follow his passion for gems and in 1975 he joined his brother selling coloured gems to jewellers in the Midwest United States. In these early years, Moriarty says that “colour was not important to most jewellers,” which made businesses like his rare in the region. “My wife Nancy and I started on our own as Moriarty Gem Corporation in 1984 and I began travelling overseas to Thailand for cut gems.” By 1994, with his passion for travelling, buying gems and selling them to retailers waning, Moriarty established his own retail store – now Moriarty’s Gem Art – in Crown Point, Indiana.

A rough garnet and its cut and polished counterpart. Image Courtesy of Steve Moriarty and Moriarty's Gem Arts.

He says: “Cutting gems, creating jewellery, custom orders and four websites is almost more than we can handle at times! I love to cut gems, this is my first priority. But to sell enough of those gems you need to do something with them, and many of the gems end up [as] unique shapes, so most everything is a custom piece. The greatest difficulty my designers and I have is we want to be artists and create our vision, but most often we have to recreate the customer’s vision, or what they saw on Pinterest or somewhere else online.”

READ MORE: Heritage Series -Maggie Campbell Pedersen FGA ABIPP

Despite this, the frustrated gem artist in Moriarty is usually restored by incredible finds and far-flung travels. When asked to describe his most inspiring trips, Moriarty points to the early 1980s, when a trip to Kenya revealed that the border to Tanzania had just been opened to American tourists. “The next day we were off on the five hour bus ride from Nairobi to Arusha, and my love of tanzanite began,” he says.

On a later trip in the early 2000s, Moriarty and his long-time travelling colleague, Jim Fiebig, discovered an “amazing cornucopia of gems” in Madagascar. He says: “There was so much amazing material that we were rejecting great gems just because they were priced a little high compared to the abundant bargains we were getting. I had many great trips to Madagascar after that, buying many of the finest quality gems I have ever owned, but never again in such quantity as the first trip.”

Today, Moriarty focuses his freeform carving attentions on Ethiopian opal, which can “require up to two full days to get a decent polish” because of the undulating surfaces.

READ MORE: Investigating Fake Rough

In addition, Rwandan amethyst, carved by Moriarty, recently appeared on the cover of Gem-A’s The Journal of Gemmology (Vol.36 No.1). Although amethyst is not high on Moriarty’s carving ‘wish list’, this material was particularly impressive. “I had been cutting Uruguay material for 20 years and considered it to be amongst the finest in the world, but when I saw the intensity of the secondary red and blues [in the Rwandan amethyst], I was hooked.”

Moriarty also mentions daylight fluorescent hyalite opal from Zacatecas, Mexico — another find that truly inspired him. After discovering some specimens at the Denver Gem & Mineral Show, he returned home and ended up cutting 7.27 carats — one of the largest faceted opals of this type. “We posted our video on YouTube just before we went to Tucson and someone shared it on reddit.com. In three days, it had been viewed over a million times. Currently, total viewing is over three million.”

Left: Hyalite opal from Zacatecas, Mexico, fluorescing in the daylight. Right: the same opal under UV light.

He continues: “I spent some time looking for hyalite opal to compare pricing, but was unsuccessful finding any cut stones in Tucson 2018. One dealer who specialises in rare gems, did give me an idea of the price [as he had] sold one of five carats. This led me to immediately call my office and have them put the hyalite in the safe and take it offline. It seems this material, discovered in 2013, was mined out by 2016 and was very unique for its characteristic of daylight fluorescence. Our next call was to the dealer who sold me the rough and we met and purchased anything of quality that he had left.”

READ MORE: Heritage Series - Let's Bragg About It!

There is an excitement to this lifestyle, of chasing down gems, that is particularly appealing to those getting started in the field. However, Moriarty also enjoys cutting his ‘old favourites’. He explains: “I love cutting garnets and although the prices for garnets of unusual colours have gone up dramatically, I still think they are under-valued. When I get done with a garnet, to me, it looks as good as any diamond I have ever seen.”

Despite his love of travelling, Moriarty is enjoying the fact that his latest obsession – Oregon sunstone – is much closer to home. And who can blame him for wanting a little more time? After all, there are gems to cut, custom orders to fulfil and a wealth of websites to be cared for… it is all in a day’s work for the Moriarty family. ■

All images courtesy of the author.

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: Cover of Gems&Jewellery Summer 2018. Image Credit: Gem-A. 

---

The Fascinating History of Antique Turquoise Jewellery

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

Read more

---

Birthstone Guide: Garnet For Those Born In January

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

Read more

---

Getting Started with Quartz Inclusions

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

Read more

---

Understanding Iridescence: Opals, Pearls, Moonstones and Fractured Stones

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

Read more

---

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

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

Read more

---

Tanzanite: The Contemporary December Birthstone

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

Read more

---

Birthstone Guide: Turquoise For Those Born In December

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

Read more

---

Understanding the Cat's Eye Effect in Gemstones

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

Read more

---

Jade and its Importance in China

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

Read more

---

Highlights of Gem-A Conference 2019

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

Read more

---

From the Summer 2018 issue of Gems&Jewellery, Gem-A gemmology tutor Beth West FGA DGA EG explores the Musica people and the emeralds of Colombia. 

There is a brooch displayed at the heart of the Geology, Gems and Minerals Gallery in the Smithsonian Institution in Washington, USA.

It is centred on a large luminous green emerald surrounded by diamonds as sharp as stars. It is undoubtedly beautiful; designed by Tiffany & Co. in the 1950s, it evokes an era of glamour and grace. But as exceptional a piece of design as it may be, the brooch is little more than a throne for the emerald that it carries.

The Hooker Emerald, named after the Institution’s principal benefactor, Janet Annenberg Hooker, weighs 75.47 carats and was originally extracted from present-day Colombia in the 16th century, when talk of the majesty of these gems had only just begun to travel.

Emerald, Composite Soude, Image Credit: Gem-A

READ MORE: Steve Moriarty on a Lifetime in Gems

The Spanish Conquistadors arrived in the ‘New World’ in the last decade of the 15th century.

When Hernan Cortez was presented with emeralds by the Aztec Emperor Montezuma II in 1519, the allure of the green gem incited the greed of the invaders and a bid to uncover their source was advanced, often leading to violence and the ultimate mistreatment of the indigenous tribes.

While emeralds became symbols of status and wealth at the end of the trade route set up by the Spanish to India and Europe, what did these stones mean to the original inhabitants of the luscious and majestic Andean terrain?

The first of the tribes’ emerald deposits was located by Conquistador, Gonzalo Jimenez de Queseda in 1537 in the village of Somondoco – home to the Muisca (or Chibcha) people.

This deposit would come to be known as ‘Chivor’, meaning ‘our farm fields, our mother’ or ‘green and rich land’ in the native tongue of the Chibcha, a reference to the emeralds un-earthed there.

Lush Colombian Landscape. Image Credit: Pixabay.com

The Muisca people were one of the four principal civilisations of the Americas.

The other three, the Incas, the Mayans and the Aztecs are perhaps more prevalent in Western thought due to the grandeur and ceremony of the architecture that remains as evidence of their complex culture.

But the Muiscas were no less advanced; they were a self-sufficient people existing in comparative isolation in the highlands of the Cordillera Oriental of the Northern Andes.

It is in this Eastern chain of peaks that pockets of the finest emeralds had formed.

READ MORE: Journal Digest, Blue Zircon from Cambodia

The abundance of the precious mineral within the Muisca’s territory, and the ability of the people to mine it efficiently, made it an important economic resource.

Markets were held regularly in conjunction with calendared festivals during which the Muisca would trade the emeralds with gold from the Guane people from north of the Chicamocha River, yopo (a hallucigenic snuff), exotic feathers and jaguar skins from the lowlands, marine snail shells, avocados and the still celebrated ‘ice-cream bean’ from their coastal cousins, the Tairona people.

Emerald in Matrix. Photo Credit: Henry Mesa. 

There is no evidence to suggest that emeralds were ranked higher in value than the other traded goods, but it is apparent that the stone held substantial symbolic weight.

In 1637, the writer Juan Rodriguez Freyle documented an initiation ceremony performed by the Muisca. On the event of a ruler’s death, the successor would be covered with a fine dusting of gold and placed on a raft at the centre of Lake Guatavita.

As music and dancing defined the shores, the new leader would throw gold and emerald votives into the lake as offerings to the Sun God.

This became known as the myth of El Dorado and rumours of a place saturated with such potential material wealth have been, from the time of its discovery to the present day, exploited by the greed of Western adventurers.

This imposition of material desire on the lands of the natives has ultimately led to wars and bloodshed over the centuries.

Emerald in Matrix. Photo Credit: Henry Mesa.

Therefore, is it perhaps worth considering the stance of the Muisca, who did not covet the emerald as their own but accepted it as a spectacular gift from the mountains, and one that they would happily relinquish to maintain harmony with the gods.

If we were to eliminate the profitability of the gem, could we too be able to see deeper into that mesmerising green? Idealistic? Perhaps. I cannot see anyone throwing the Hooker emerald into a lake any time soon. ■

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: Emerald with Quartz. Image Credit: Henry Mesa.  

---

The Fascinating History of Antique Turquoise Jewellery

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

Read more

---

Birthstone Guide: Garnet For Those Born In January

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

Read more

---

Getting Started with Quartz Inclusions

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

Read more

---

Understanding Iridescence: Opals, Pearls, Moonstones and Fractured Stones

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

Read more

---

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

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

Read more

---

Tanzanite: The Contemporary December Birthstone

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

Read more

---

Birthstone Guide: Turquoise For Those Born In December

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

Read more

---

Understanding the Cat's Eye Effect in Gemstones

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

Read more

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Jade and its Importance in China

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

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Highlights of Gem-A Conference 2019

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

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Getting to grips with The Journal of Gemmology Volume 36, No.3, Guy Lalous ACAM EG offers us an edited breakdown of a feature on Bumble Bee Stone from West Java, Indonesia. 

Bumble Bee Stone (BBS) is an attractive bright yellow-to-orange and black patterned gem from West Java, Indonesia. Production has been ongoing since 2003, yielding an estimated 150 tons of lapidary material. 

The paper in The Journal of Gemmology reports on the location, geology and gemmological properties of BBS, focusing on the cause of its extraordinary colouration. 

The mining area for BBS is situated on the lower slopes of an active volcano, Mt Ciremai (or Cereme), which is located about 25 km south-west of the coastal town of Cirebon in West Java.

What is a solfatara?

A solfatara is a volcanic area producing hot vapour and sulfurous gases.  The name is derived from the Solfatara of Pozzuoli a volcano part of the Campi Flegrei (Burning Fields) near Naples. 

BBS was formed within a solfatara (a fumarole that vents gases rich in sulphur) occurring in close proximity to the Mt Ciremai volcano.

This type of vent is common near active stratovolcanoes, and results from the heating of circulating groundwaters containing various elements or compounds extracted from the volcanic system—in this case iron, sulphur, calcium carbonate and arsenic.

Figure 2. The BBS deposit is located at the base of Mt. Ciremai, an active volcano, in the vicinity of Kuningan, West Java, Indonesia. 

Such a system produces abundant ‘sooty’ pyrite, consisting of very small crystals of the iron sulphide, crystallising rapidly near the surface, which looks like black soot.

As the gases escape the solfatara, minerals are deposited as more-or-less regular bands in fractures within the volcanic rock, which is here comprised of fine-bedded volcanic ash and intercalated pyroclastic tuff (an accumulation of volcanic ejecta of varied size).

The veins are near vertical, with individual colour bands rarely exceeding 5 cm. The tuffaceous wall rock contains marcasite, an iron sulphide that is unstable when exposed to air and moisture.

After about 1–2 weeks in this environment, the breakdown of marcasite facilitates the separation of BBS vein material from its volcanic host rock.

 
Figure 3. The pulverulent appearance of the colour banding in BBS is shown here under magnification in sample no. 1591.
Left: Yellow-to-orange pigment is disseminated within the carbonate matrix, forming colour bands, within with micro-geodes are found. 
Right: The black pigment forms minute discs that are resolvable only at higher magnification. Photomicrographs by E. Fritsch. 

The gemmological properties of the material are reported. Refractive index values were difficult to measure because of the material’s porosity.

Specific gravity varied between 2.42 and 2.74; the average of seven measurements was 2.57. Bubbles appeared when a drop of diluted hydrochloric acid was placed on the surface, confirming that this material is carbonate rich.

Therefore, it is not jasper, which is an opaque form of microcrystalline quartz. When examined with the binocular microscope, the appearance was that of coloured powders cemented in the carbonate matrix.

Small cavities were actually micro-geodes; many contained very small crystals that were orange or tended towards red. Visible-range reflectance spectra for the various coloured areas of BBS revealed that the yellow regions have an absorption edge at ~530 nm, the colour perceived is a combination of all wavelengths above 530 nm (green), which is observed as yellow. 

The absorption edge shifted towards 550 nm in the orange areas which is logical as less yellow equates to more red. The black portions showed a nearly flat spectrum.

What about pararealgar?

Pararealgar is a bright yellow monoclinic polymorph of realgar, a more common and better-known red arsenic sulphide, which is also monoclinic but with a different class of symmetry.

The Raman spectra of all analysed samples presented bands for calcite at about 285 and 160 cm^–1. Aragonite bands were found in only one part of one orange sample. In ‘mustard’-to-yellow parts, additional major bands were recorded at about 346, 284, 233 and 157 cm^–1.

They correspond to pararealgar, which has the formula As₄S₄. The Raman spectrum of realgar dominated the bright orange areas and the reddish crystals in the micro-geodes mentioned above, with main peaks at approximately 355, 221, 194 and 184 cm^–1.

It had a much higher Raman scattering intensity than pararealgar, thus it dominated the spectrum of a mixture of both polymorphs.

As such, the orange areas appeared to be a mixture of pararealgar and realgar. In the black areas, a small Raman signal appeared at about 378 cm^–1. The closest signal we could find is pyrite, FeS₂, which has a strong doublet at 385 and 355 cm^–1.

Figure 5. The Raman spectra of the BBS samples tested always showed peaks for calcite, with additional features corresponding to pararealgar and realgar in yellow and orange areas. The spectrum shown here for realgar is from a reference crystal, as no area of BBS we analysed consisted of pure realgar.

What about framboidal pyrite?

The term framboid describes an aggregation of uniformly-sized particles of the same mineral, from the French framboise for raspberry, as this berry is composed of aggregated uniformly sized drupelets.

Figure 6. The three polished specimens of BBS on the left (12–26 cm long) show spectacular orbicular (also called ‘bull’s-eye’) patterns with a strong colour contrast. The typical bull’s-eye pattern ranges from 10 to 14 mm in diameter, but may be much larger (see Figure DD-1 in The Journal’s online Data Depository). Such pieces are derived by cutting across botryoidal areas such as shown by the BBS slab on the right. The colourless calcite crystals (up to ~3 cm long) induce the botryoidal structure in the overlying sulphide-bearing layers. Photos by J. Ivey.

Scanning Electron Microscopy and Microanalysis were performed on the material.

The nearly ubiquitous presence of Ca confirmed that the material is mostly calcite, although the consistent presence of a small Mg peak suggested it was a slightly magnesian calcite.

Yellow-to-orange areas were rich in S and As. The black discs were composed of circular aggregates with maximum diameters ranging from ~5 to 30 μm.

They were composed of micrometer-sized crystals identified as pyrite. Their morphology varied, from nearly cubic (square faces) to cubo-octahedral (pseudo-hexagonal faces) to octahedral triangular faces. This is reminiscent of framboidal pyrite.

What about botryoidal concretions?

A concretion is a compact mass of a mineral formed by precipitation within the spaces between sediment layers. Botryoidal refers to the crystal shape resembling a bunch of grapes. 

BBS belongs to a rare category of gems coloured by micro-inclusions of sulphide pigments.

Its most remarkable characteristic is a bright yellow colour, which is caused by the presence of an unexpected sulfide, pararealgar. The orange colour in some samples consists of a mixture of pararealgar and realgar. Both minerals are polymorphs of As₄S₄, arsenic sulphide.

This is not the first time that pararealgar has been identified as the colouring agent in a gem material. Gaillou (2006) documented this pigment via Raman scattering in a little-known bright yellow opal from the area of Saint Nectaire in central France.  

BBS is currently a single-source gem material, with no other deposit having been documented elsewhere.

The most sought after is an orbicular variety with a typical bull’s-eye pattern, obtained by slicing across botryoidal concretions.

This is a summary of an article that originally appeared in The Journal of Gemmology entitled ‘Bumble Bee Stone: A Bright Yellow-to-Orange and Black Patterned Gem from West Java, Indonesia’ Emmanuel Fritsch and Joel Ivey 2018/Volume 36/ No. 3 pp. 228-238

Cover Image: These cabochons (up to 40 mm long) and rough pieces of Bumble Bee Stone (BBS) were produced in 2017, the samples are more orange than previously mined material.  
Photo by J. Ivey.

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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The Fascinating History of Antique Turquoise Jewellery

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

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Birthstone Guide: Garnet For Those Born In January

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

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Getting Started with Quartz Inclusions

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

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Understanding Iridescence: Opals, Pearls, Moonstones and Fractured Stones

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

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

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

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Tanzanite: The Contemporary December Birthstone

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

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Birthstone Guide: Turquoise For Those Born In December

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

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Understanding the Cat's Eye Effect in Gemstones

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

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Jade and its Importance in China

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

Read more

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Highlights of Gem-A Conference 2019

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

Read more

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幸運なことに１月に生まれた方は、美しく、明るく、鮮やかなガーネットが誕生石です。虹色 の宝石、ガーネットは実に様々な色をもつ鉱物で、業界では処理を行わないごくわずかな宝石 の一つに数えられます。

ガーネットは様々な彩度、種類、色相がある絵具のパレットのようであり、豊かな歴史と伝説 があることでも知られています。ヴィクトリア時代の王族、古代エジプト時代の歴代王、古代 ローマ人をはじめ、多くの時代で好まれた宝石です。

きれいなホーステール・インクルージョンが見られるデマントイド・ガーネット。写真：Pat Daly

ガーネットの色

ガーネットは赤色部に強いスペクトルもち、ざくろの実を思い起こさせるような赤褐色を帯び たオレンジ、濃いバイオレット、ロイヤル・レッドの色合いを示します。「ガーネット （garnet）」は14世紀中期に使用されていた濃い赤色を意味する英語の「gernet」にちなみ、 さらにはラテン語の「ざくろの実（種）」を意味する「グラタナス（granatum）」に由来する 名前です。これはガーネットの結晶がざくろの種や濃い赤色に似ているためです。ガーネット とは、赤色のパイロープ・ガーネットから趣のある緑色をしたツァボライト・ガーネットまで 、鉱物のグループを指す用語です。

ガーネットの色が様々であるのは、マンガン、鉄、クロムなどの微量金属によるものです。ガ ーネットの変種で異なる化学組成は、硬度に6.5－7.5の範囲をもたらす原因となります。

偏光器下でのガーネットとペリドタイト。写真：Pat Daly

左： フェザー・インクルージョンを伴うスペサルティン・ガーネット。右:結晶インクルージ ョンを伴うヘソナイト・ガーネット。写真：Pat Daly

ガーネットの種類

ガーネットには、同じ結晶構造にもかかわらず、若干異なる化学組成をもつ5つの主な変種があ ります。

• アルマンディン：紫色から帯橙赤色
• パイロープ：紫色から帯橙赤色
• スペサルティン：橙色から黄色
• アンドラダイト：黄色から帯黄緑色
• グロッシュラー：無色から黄色、帯橙赤色、鮮やかな緑色（稀少）

ガーネットはどこで採れるのか？

ガーネットはオーストラリア、インド、チェコ共和国、ミャンマー、ブラジル、スリランカな ど世界中の多くの国々で見つかります。19世紀にはジュエラーのピーター・カール・ファベル ジェ（Peter Carl Fabergé）が製作した多くの作品にガーネットが用いられ、ロシアの王族に愛 されました。ボヘミアやロシアは19世紀の最初のガーネットの産地として記録されていますが 、現在では、タンザニアやナミビアでガーネットが豊富に採取されます。

デマントイド・ガーネットのホーステール・インクルージョンを拡大した写真。写真：Pat Daly

ガーネットの歴史と古代の伝説

ガーネットには長い間語り継がれてきた歴史と多くの言い伝えがあります。「誠実の宝石」と して知られるガーネットは健康、繁栄、平和の力をもち、この石を身に着ける者は善い行いを して報われると言い伝えられてきました。鮮やかで強い印象をもつガーネットは、活気に満ち た1月に生まれの方に相応しい石であると考えられています。そして、ガーネットを着ける 人は新たな目標をもち、希望と幸福を感じながら新年を迎えることができるとされています 。

また、戦いに臨む人々は勝利と身の安全を祈る護符としてこの宝石を使いました。多くの戦士 たちが病気や貧窮を防ぐために身に着け、戦いで負った傷に石を当て、治癒を促すものとして 使用しました。さらに歴史を遡ると、エジプトではガーネットを生命の象徴としてジュエリー や彫刻に象嵌しました。古代ローマ人は好んでガーネットをシグネット・リング（印章付きの 指輪）に用いました。これは石に沈み彫りを施し（インタリオ）、重要な文書に封印をするも のです。健康にも効果があるとされたため、歴史を通じて聖職者や貴族階級の間で珍重され続 けました。

マリ産のガーネット。写真：Pat Daly

今日、ガーネットはリング、ペンダント、ティアラなど様々なジュエリーに使用されています 。その色と透明度が、作品を価値ある素晴らしいものに仕上げているのです。

ガーネットが使われた大変有名なジュエリーの例として、ヴィクトリア時代に製作されたスミ ソニアン・パイロープの髪飾り（the Smithsonian Pyrope Hair Comb）が挙げられます。頂上の 中央石を取り囲み、ティアラの形をした髪飾りを装飾するパイロープ・ガーネットは、ボヘミ アの鉱山（現在のチェコ共和国の一部）で採取されたものです。このローズ・カットを施した ガーネットはメッキをした金属またはイエロー・ゴールドにセットされました。この作品が流 行したヴィクトリア時代には人気のあるスタイルでした。

今年の成功を祈る護符として、また1月生まれの方への贈り物として、個性的なガーネットのフ ァイアと煌めきは、強く感情を揺さぶり、時を超えた美しさをもつことでしょう。

 針状のルチル・インクルージョンを伴うマラヤ・ガーネット。写真：Pat Daly

表紙：結晶インクルージョンを伴うアルマンディン・ガーネット。写真：Pat Daly ©Gem-A

The typical image of a diamond tends to be of a clear and colourless stone, therefore it is hardly surprising that these are presumed to have the highest monetary value. In reality, diamonds can present as a range of different colours and uniquely-coloured diamonds can command premium prices.

Coloured diamonds are created when impurities or deformities occur in a diamond’s lattice of carbon atoms, with particular impurities resulting in different colour formations.

The most valuable stones will be those which are purest in colour, most saturated and most even in tone. In order to assess the grades of colour, coloured diamonds are placed into one of nine categories: faint (least valuable), very light, light, fancy light, fancy, fancy dark, fancy intense, fancy deep and fancy vivid (the rarest and most expensive).

The Aurora Pyramid of Hope Collection contains the full spectrum of natural diamond colours.
Image copyright Trustees of NHM, London.

Increasing rarity leads to higher retail prices and by examining the variations between some notable types of coloured diamonds, we can see a clear scale of value emerging based on an agreed-upon grading system.

Inspired by Pantone’s ‘Color of the Year 2019’, Rui Galopim de Carvalho FGA DGA dives into the underwater world of precious coral and addresses some of the misunderstandings around its use in the jewellery industry.

The colour of many precious corals has been announced as the ‘Color of the Year 2019’ by Pantone, the US-based company known for its proprietary colour system widely used in the printing industry. Under the name ‘Pantone 16-1546 Living Coral’ this colour code alludes to the pink to red colour that is commonly associated with corals. A clarification is therefore in order to properly understand what it is meant by coral in the jewellery industry.

Coral is the collective name that has been used to describe a very large number of species of cnidarians of the Anthozoa class. Among these more than 7,300 species, we encounter the endangered shallow-water coral species in Australia’s Great Barrier Reef and elsewhere that have been suffering from bleaching and death as a result of climate change and ocean acidification.

Read more: Understanding the 'Coral Conversation'

This dramatic situation for the equilibrium of the planet’s marine ecosystems has negatively impacted on the reputation of coral as a luxury product. It happens that the corals used in the jewellery industry do not live in the same ecosystem as those endangered reef corals. This is why those that are used jewellery and decorative arts have been designated as ‘precious corals’ by CIBJO, the World Jewellery Confederation, separating them from the ‘common corals’ and even more dramatically from the endangered reef corals.

What are Precious Corals? 

These are corals most used in high-end jewellery and decoration and are limited to species belonging to the Corallidae family, particularly from the genus Corallium, Pleurocorallium and Hemicorallium. It is in some of these groups that we can find the red and pink, sometimes salmon-coloured and often white varieties with porcelain like lustre after polishing that relate to this year’s Pantone colour.

A parcel of polished small branches of Deep Sea coral (Hemicorallium laauense). Photo courtesy of Liverino 1894.

Although a few varieties of red and pink coral were listed for the monitoring of the trade in Appendix III of CITES at the request of China in 2008 (Corallium elatius, C. japonicum, C. konojoi and C. secundum[sic]), no precious corals are listed in the more restrictive CITES Appendixes I and II.

It must be said that the recommendation for monitoring expired in 2013, being extended until 2016, and that for the next CITES meeting in 2019, no further action is to be proposed for precious corals. Current fishing regulations in the Mediterranean, Taiwan and Japan have played an important role in resource management of precious corals and more initiatives are being implemented to further the issue.

Let’s then establish what are the precious coral species currently recognised by the trade:

Corallium japonicum (Aka, Moro or Oxblood coral), the dark red to very dark red corals with a lengthwise white interior which live at depths of 80 to 300 in Japan

Pleurocorallium elatius comprising of two varieties: the so called Momo, Cerasuolo or Satsuma coral, a bright red, salmon, orange and flesh colour with a lengthwise white interior and its albino variety, known in the trade as Angel Skin, Boké or Magai coral, a delicate flesh pink, with different colour intensities, which live at depths of 150 to 300 meters mainly off the coasts of Japan and Taiwan

Pleurocorallium konojoi (Pure White or Shiro coral), the milky white and sometimes with red or pink specks, that live at depths of 80 to 300 meters in the South China Sea and off the coast of Hainan

Pleurocorallium secundum (Midway, Rosato or White/Pink), the veined white or pink, and sometimes with red specks, or uniform clear pink, that lives at depths of 400 to 600 meters off the coasts of Hawaii and Midway Island

Hemicorallium laauense (Deep Sea or Shinkai coral), the bright white, clear pink or white pomegranate with red veins or spots which live at depths of 1000 to 2000 meters off the coast of Midway Island, north-west of Emperor Seamount

Hemicorallium regale (Garnet coral), the pomegranate colour with different shades of uniform pink that live at depths of 350 to 600 metres off the coast of Hawaii

Hemicorallium sulcatum (Misu, Missu or Miss coral), the pink to violet uniform colour which live at depths of 100 to 300 metres in the Philippines northern coastal waters

Corallium rubrum (Sardinian or Mediterranean coral), the historically and culturally famous uniform red with medium to strong saturation that live at depths up to 1,000 metres (harvested only bellow 50 meters) in the Mediterranean and in the Atlantic Ocean off the coast of North Africa, including in the waters of the Canary Islands and Cape Verde
The taxonomy of precious corals (in Pantone 'Living Coral' colour) and Common corals (in grey).

What are Common Corals? 

Apart from the above mentioned Corallidae family species, there are a few other corals that have been used for decoration and in jewellery. These, defined as common corals, include mostly calcareous types, like sponge corals, bamboo corals and blue corals as well as black and golden corals, which have non-calcareous exoskeletons. Many of these must undergo treatment (e.g. bleaching, dyeing, impregnation) to be used as gem materials.

Contrarily to precious corals, certain common coral species are listed in CITES Appendix II, e.g. black coral (Antipatharia spp.), blue coral (Heliopora coerulea), stony corals (Scleractinia spp.), organpipe corals (Tubiporidae family), fire corals (Milleporidae family) and lace corals (Stylasteridae family).

Reef coral preservation should be on the top of the agenda not only of the jewellery industry but also of society as a whole, mainly by reducing the carbon impact of civilization that is responsible for climate change and ocean acidification.

The dramatic effects of bleaching in coral reef (before and after). Image courtesy of The Ocran Agency / XL Catlin Seaview Survey/Coral Reef Image Bank.

CIBJO recently argued through its Coral Commission president Vincenzo Liverino under the banner of a ‘Promise of Sustainability’ at the 21st FEEG Symposium and CIBJO Seminar on Responsible Sourcing and Sustainability held at the VicenzaOro show, Italy in January, that it is a task of the industry and first of all of the coral industry to set an example by embracing the ‘Jewellery Industry Measurement Initiative’ promoted by CIBJO to help companies within the jewellery industry understand their environmental impact, reduce their carbon footprint, and protect themselves and the industry as a whole.

The need for education of both the trade and the consumer in these matters is therefore of prime importance to correct what was a lack of consistency in the terminology used to describe precious coral, to inform the public of about the biology, ecology, history and legacy of precious coral and to raise public awareness of issues related to the sustainability of coral in general, and precious coral in particular, predominantly in light of the challenges posed by global warming and ocean acidification.

Do you want to broaden your knowlege of organics and gemstones? Discover Gem-A Short Courses and Workshops, or explore our Gemmology Foundation and Diploma Courses. 

This article was first published in the Spring 2019 edition of Gems&Jewellery. To find out more and read the magazine archive online, please click here. 

Cover image: Two necklaces: Angel’s skin (Boké or Magai) coral, the albino variety of Pleurocorallium elatius, and Oxblood (Aka or Moro), the deep red variety of Corallium japonicum. Image courtesy of Chii Lih Coral.

Images courtesy of the author unless otherwise stated.

Gems&Jewellery is delighted to welcome jewellery historian and valuer, John Benjamin FGA DGA FIRV as our columnist for 2019. As part of a new Gemstone Conversations series, John explores the history of the use of garnet in antique jewellery and tells us why we should give more credit to this special yet undervalued gemstone.

I have often thought that garnet is a rather underappreciated stone. True, it is extremely common and turns up in everything from ancient gold rings to cheap, modern, mass-produced bijouterie — but this misses the point, which is that the sheer beauty and versatility of garnet meant that right up to the beginning of the 20th century it was consistently one of the most popular of all gemstones used in decorative jewellery.

Historic Uses of Garnet in Jewellery

Garnet was esteemed by the Romans at a time when a vivid gemstone conveyed wealth and status. Fine examples were polished into cabochons or cut into cameos and intaglios depicting classical figures or deities. By the 5th and 6th century garnet was often the stone of choice with small, simple, domed or faceted examples providing a decorative embellishment to Anglo Saxon brooches, pendants and buckles.

A Neo-Renaissance gold 'Holbeinesque' pendant mounted with a pyrope garnet cabochon in a champlevé enamelled frame set with chrysolites, circa 1870. Image courtesy of Woolley & Wallis.

Garnet Jewellery of the 17th Century 

No doubt because of its widespread availability it was frequently set into medieval rings and ornaments and by the late 16th and 17^th century its sheer abundance and desirability led to it being used throughout Europe in everything from rings and earrings to opulent pendants, usually accompanied by colourful, polychrome enamel and gold mounts.

Many of these Renaissance and later garnets were polished into large and irregular-shaped hollow-back cabochons known as ‘carbuncles’ and were usually rich, purplish-red almandines from India and Ceylon. There are quite a large number of these garnets on display in the incomparable Cheapside Hoard at the Museum of London.

Read more: Garnet for those Born in January

For me, part of the allure of garnet is the broad range of colours available and I have always admired hessonites, not only for their rich, orangey-brown colour but also for their interesting ‘treacle-like’ inclusions. Since garnet is a reasonably hard gemstone it provides an excellent cutting surface, so from the 16th to the 18th century hessonite (known in those days as ‘Jacinth’ or ‘Hyacinth’) was a popular stone for fashioning into cameos or setting into bracelet clasps.

The Golden Age of Garnet Jewellery

Undoubtedly, it was the late 18th and early 19th century when garnet really came into its own. Flat-cut almandines of cushion, pear and circular shape were artfully set into parures comprising a necklace, a pair of bracelets, earrings and a brooch. Foiling the stones and fully enclosing the mounts at the back intensified their glowing appearance, especially when illuminated in candlelight.

A Georgian gold and flat-cut almandine garnet parure comprising a necklace, earrings, maltese cross and brooch, circa 1800. Image courtesy of Woolley & Wallis.

The use of garnet in moderately priced jewellery continued through the 19^th century reaching a peak of popularity in the 1870s when ‘Holbeinesque’ jewellery – pendants and earrings of a design inspired by the look of the Renaissance – resulted in large pyrope cabochons being set in colourful, champlevé-enamelled frames often accompanied by compatible gems such as diamond or chrysolite. This was the so-called ‘Grand Period’ of jewellery manufacture and the rich, vibrant colour of garnet provided the perfect vehicle for showing off bold and distinctive bracelets, brooches and necklaces.

Read more: Questions to Ask When Buying a Piece of Gemstone Jewellery

Handmade craftsmanship gave way to mechanical, repetitive mass production at the end of the century. Garnet continued to be used in cheap central European jewellery often accompanied by inexpensive colourful gems especially turquoise, pale green beryl and pearls in poor quality, silver gilt settings.

At the same time jewellers in Czechoslovakia (now Czech Republic and Slovakia) began to set clusters of small simply faceted pyropes in base metal thus providing colourful but affordable bangles, brooches and earrings for the mass market. These ‘Bohemian’ garnets are very much of their time and are still very common today.

A 'Bohemian' garnet cross circa 1890. Versatile and inexpensive, these colourful jewels were extremely common at the end of the 19th century. Image courtesy of Woolley & Wallis.

Demantoid Garnet Jewellery 

There was, however, one last moment of glory for garnet. Demantoid, the bright green variety of andradite garnet, had been discovered in the Russian Urals as far back as 1853. Nevertheless, it was not until the 1880s that it started to be set commercially in jewellery and accessories, firstly by Peter Carl Fabergé and subsequently by jewellers in London who obtained supplies from gem merchants such as E W Streeter.

The naturalistic green tones and adamantine lustre of demantoid perfectly conveyed the look of a reptile’s skin or an insect’s body, resulting in a surge of popularity in novelty brooches designed as frogs, lizards and dragonflies. 

A Demantoid garnet and diamond dragonfly brooch, circa 1880. The naturalistic colour of this ever popular variety of andradite garnet resulted in a wide range of novelty insect and reptile brooches appearing on the market at the end of the 19th century. Image courtesy of Woolley & Wallis.

This article and images were originally published in the Spring 2019 issue of Gems&Jewellery. Gem-A Members can read the issue here.

Cover Image: Late 18th/early 19th century Neoclassical hessonite cameo ring of the Emperor Tiberius. Images courtesy of Bonhams.

We are thrilled to announce that the Gem-A Photographer of the Year competition is back for 2019!

With new rules, a new judging process, and fantastic new prizes, this year’s competition promises to be our biggest and best yet. What’s more, while the competition had traditionally only been open to Gem-A Members and students, we are now happy to accept entries from anyone with an interest in gemmology and a passion for photography.

We are very excited to see what marvels this year’s competition will bring as we have decided to forego categories; instead, we want to see entries that display your own unique interpretation of gemstones, gemmology and the wider trade.

You might decide to share a photograph of a piece of jaw-dropping jewellery, or maybe you have captured the hidden, intricate beauty of a particular gemstone through photomicrography? Or perhaps you have shot a spectacular scene while gemstone mining or trading on a recent trip abroad?

Whatever highlights an unusual or insightful facet of our sector, we want to see it!

Why Enter?

Win the chance to have your photograph featured in Gems&Jewellery. Winners could be featured on our cover, our Last Impression or our Big Picture feature page.

You can add the accolade of being named Gem-A’s Photographer of the Year to your portfolio.

Entry is free and open to all.

2017 Overall Winner - Dandelion flower in sapphire. Growth blockage with thin film rosette in Sri Lankan sapphire using modified Rheinberg illumination. Field view of 1.34mm. Image by Jonathan Muyal FGA.

The Prize:

The overall winner will be gifted a £300 voucher to spend at Gem-A Instruments and one year’s free Membership of Gem-A.

Two runners up will win a £50 Gem-A Instruments voucher.

All three winning entries will see their photographs published in Gems&Jewellery magazine.

The competition is open now and we shall be accepting entries until August 30, 2019. The winner will be announced on Gem-A’s Facebook page shortly after the competition has closed.

For the Competition rules and details on how to enter click here. Good luck!

Cover image: 2017 entry - Frog in Amber from the Dominican Republic. Image by Anthony Shih FGA DGA.

Interested in developing your gemmological knowledge? Have a look at our upcoming one-day workshops.

Treasured the world over for their timeless elegance, lustre and iridescent multi-tonal colours, pearls have been a favourite of high-end jewellers and collectors alike for hundreds of years. 

The majority of gem-quality pearls are produced by bivalve molluscs (an animal whose shell has two hinged parts), but they can also be produced by gastropods (a single shell) which are more rare and may come at a higher price. A pearl is created when an irritant agitates the body of a mollusc and initiates the growth of nacre, a substance that is created by platy crystals of aragonite (a calcium carbonate mineral) held together by an organic compound known as conchiolin.

Well-shaped, naturally occurring specimens can be very rare and highly expensive – in 2017, a natural pearl and diamond drop pendant sold for US$1,452,500 at a Bonhams auction. Cultured saltwater and freshwater pearls are far more abundant and can be cultured to produce excellent lustre in a variety of colours and sizes. But what are the main differences between saltwater and freshwater pearls, and what are the key characteristics that make the highest quality and most desirable specimens?

Saltwater Pearls

Saltwater pearls are produced by oysters found in the sea and generally only a single pearl per shell is found. As natural saltwater pearls are extremely difficult to come across, cultured specimens make up the vast majority on the market. Cultured saltwater pearls are farmed with a bead nucleus made from shells of freshwater molluscs (mussels) as these varieties tend to have thicker shell sections which are ideal for fashioning into a sphere.

Akoya Pearls 

Kokichi Mikimoto perfected the process for culturing pearls in Japan in the 1890s, utilizing Akoya pearl oysters. Akoya pearls are characterised by their very bright lustre and usually white body colour, often enhanced by bleaching. Pink, silver, blue and yellow shades can also occur naturally. Akoya pearls will normally have a diameter of 6-8 millimetres.

Read more: Pearls for Those Born in June 

Grey and black saltwater pearls are highly desirable and have been known to fetch stellar prices at auction. The Cowdray pearl necklace, a string of 42 natural grey saltwater pearls once owned by Viscountess Cowdray, broke the auction record for the sale of a pearl necklace when it sold for US$5.3 million at Sotheby’s Hong Kong in 2015. 

South Sea Pearls 

South Sea pearls can also be cultured, and although natural specimens would be infinitely more valuable. Cultured South Sea pearls have been known to reach astronomical prices at auction. In 1992 a strand of 23 Australian South Sea pearls sold for $2.3 million at Sotheby’s Geneva. Among the larger of saltwater varieties, they will typically reach 11-14mm in diameter but in some cases they can grow much larger. Part of the desirability of South Sea pearls may be the iridescent gold and silver hues they acquire from the silver-lip and gold-lip molluscs in which they grow.

Tahitian Pearls 

Cultured in a black-lip oyster, Tahitian pearls have a darker nacre with surface iridescence and overtones of peacock, blue, green, purple and gold. Tahitian pearl quality is regulated by the French Polynesian government exerting tight controls to ensure consistent, quality material reaches the market.

Cortez Pearls 

Originating from rainbow-lipped molluscs found in the Sea of Cortez in Mexico, Cortez Pearls are dark in body colour and display a fabulous rainbow iridescence on the surface. Furthermore, these pearls are somewhat unique as they are the only variety which can show an unusual red fluorescence when exposed to long wave ultra violet light.

Fiji Black Pearls 

Another highly desirable variety of saltwater pearls are Fiji black pearls. Among the rarest types of pearls in the world, they are also a relatively new variety, having first entered the industry in the 1960s. Since then, their introduction by J. Hunter Pearls in 1999 has increased and expanded their market. As a result, we can now see Fiji pearls in a range of vivid colours including gold, peacock, green and chocolate, and although they only have a small yearly output, they command premium prices. 

Freshwater Pearls

Freshwater pearls are grown in rivers and ponds using mussels, and many pearls can be grown within a single shell in a much shorter time that saltwater counterparts. Although freshwater pearls can occur in various colours, white, pink and pastel shades are by far the most common.

There are two ways in which freshwater pearls can be cultured; they can be tissue-nucleated, which means that a small piece of foreign mantle is grafted into the host. This process will usually result in a baroque-shaped pearl.

Cultured freshwater pearls can also be bead-nucleated in the same way as saltwater pearls. Shapes range from round to unique baroques with names like fireball, soufflé and Edison.  However, other shapes are possible, including star, coin and heart. Colour, lustre and size are the most important value factors but they tend to be less lustrous than Akoya pearls.

Considering Value

When considering purchasing freshwater and saltwater pearls, whether natural or cultured, there are five key aesthetic features to take into account in order to make a good investment:

Pearl size

The general rule is the bigger the pearl, the higher the value.

Pearl lustre and orient (shine)

Lustre is a key factor for the majority of cultured pearls and it relates to the amount of light return from the surface of a pearl. Orient is the iridescence of the pearl, a subtle feature created by dispersion of light between platy crystals of aragonite creating different tones.

Pearl colour (shade)

White is a timeless favourite but the value of particular colours is driven by what is popular in fashion at any given time.

Pearl shape

A perfectly spherical shape is always most valuable for pearls.

Pearl surface condition

A near perfect surface condition free from blemishes such as bumps, dimples, scratches and spots will significantly raise the value and market desirability of a freshwater or saltwater pearl.

Read more: Radiocarbon Age Dating on Natural Pearls

While it would always be a very special and rare treat to be able to purchase a set of lustrous, natural round pearls, high quality cultured pearls can make equally, if not more, stunning jewels and a very good investment, particularly when mounted in fine settings from luxury jewellers; exquisite pieces from Harry Winston, Van Cleef & Arpels and Buccellati have recently fetched tens of thousands dollars at auction.

In spite of such awesome prices, the great thing about pearls is that they can be one of the more affordable gemstones to purchase and seem to perennially exude glamour and luxury. If you look out for quality, size, lustre, colour, shape and surface, you are sure to find a fabulous and timeless jewel.

Interested in developing your knowledge about gemstones? Have a look at our upcoming workshops.

Cover Image: 12-13mm South Sea pearls, 0.38ct of diamonds, set in 18ct white gold. Part of the Yoko London Classic Collection. All images courtesy of Yoko London: www.yokolondon.com 

アンドリュー・フェローズ FGA DGAが、世界で最も有名な宝石コレクションである「クラウン・ジュエル」にまつわる神話や伝説を見ていきます.

有名なクラウン・ジュエルCrown Jewels が収められているロンドン塔の基礎は、征服王ウィリアムによって1066年に築かれました。そして、代々の君主たちによって改造や修復が重ねられ、13世紀後半までには今日見られる大体のレイアウトが確立しました。ヨーロッパで唯一現存するクラウン・ジュエルは141以上の宝物で構成され、何百年もの間ロンドン塔の中で安全に保存されてきました。これらは毎年、多くの観光客を惹きつけています

このコレクションには、単に宝物の美しさを堪能する価値があるだけでなく、宝石類の背後にある魅惑的な物語と歴史について学ぶ価値もあります。

帝国王冠（インペリアル・ステート・クラウン）

帝国王冠（インペリアル・ステート・クラウン）―コレクションにおける最も有名な王位の象徴― は、即位式終了後に君主が頭上に戴くもので、議会の開会の際にも使われます。王冠には、このような重要な行事に際して、王冠自体と同じくらい凝った専用の儀式用馬車が用意されています。王冠は実に3.17kgもの重量があり、短い間のみかぶることができます。

ジョージ4世が1821年に戴冠した際、王冠の重さが理由で歯痛になったという逸話があります！王冠にはロイヤル・コレクションにおいて重要な宝石がいくつか使われており、その多くには非常に面白い物語があります。

黒太子のルビー

多くのジェモロジストがよく知っている物語の一つとして、黒太子のルビーが挙げられます。これは、最も美しい宝石であると同時に最も不吉な石といわれています。そればかりか、完全に誤った名がつけられています。ルビーと呼ばれていますが、実際は非常に大きな宝石品質のレッド・スピネルです。この宝石は、デューク・オブ・コーンウォール、プリンス・オブ・アキテーヌと呼ばれ、「黒太子」とも称される14世紀のプリンス・オブ・ウェールズであったエドワード皇太子（エドワード・オブ・ウッドストック）に贈られました。

王冠の前部のカリナンIIより上にあるクロスパティー（末広十字）についているこのスピネルには、黒い、血の歴史があります。14世紀に書かれた最初の記録によると、ムーア人の皇太子であったアブー・サイードがこの石を所有し、ペドロ残酷王が征服していた軍隊に引き渡そうとしますが、彼は休戦旗の下で待ち伏せされ、奪われたこの大きなスピネルで処刑されました。これがまさに血の軌跡の始まりです。その後、ペドロは軍事援助のための頭金としてこの石をエドワード皇太子に差し出しました。支払いの残りは宝物と宝石から成ると思われていましたが、決して支払われることはありませんでした。そして、結局、ペドロは彼の異母兄弟に待ち伏せられて刺し殺されました。

後にこの石は、1415年のアジャンクールの戦いで、ヘンリー5世のヘルメット（兜）につけられ、言い伝えによると石が彼の命を救ったとされています。斧で彼の頭が強打されたときそのヘルメットは破壊されたものの、彼を死に至らしめることはありませんでした。「ルビー」は粉砕されたヘルメットから取り出され、ヘンリー5世が亡くなるまで手元に置かれました。残念なことに、リチャード3世に関しては同じことは起きませんでした。彼もまた1485年のボズワース・フィールドの戦いのとき、「ルビー」をヘルメットにつけていました。おそらく、彼は石が身を守ってくれる、運をもたらすと思っていました。しかし、悲しいことに、彼は戦場で死んでしまいます。この同じ「ルビー」は後にチャールズ1世によって売却されるまで、ヘンリー6世とエドワード4世の王冠、ヘンリー8世（彼は石をを襟に着けていた）に使われました。そしてこの石は王室に戻りチャールズ2世の王冠に用いられ、その後ジョージ4世の即位式で使われました

聖エドワードのサファイア

また、帝国王冠の上部の十字架には、サファイアがセットされています。伝説によれば、このサファイアは、かつて証聖王エドワード（信仰のあつい英国王）の即位の指輪（コロネーション・リング）につけられていました。ある夜、エドワードがウェストミンスター寺院の前を通ると、一人の乞食に遭遇しました。彼は持っていたすべてのお金をすでに寄付してしまっていたので、深く考えずにその乞食にサファイアのついた指輪を与えました。

数年後、2人のイングランド人が聖地巡礼中、嵐に襲われました。その時1人の老人が彼らに近づいてきました。そして、2人の男がイングランド人であること、エドワードが今も国王であることを聞き、その老人は彼らに嵐の避難所を提供しました。翌朝、彼らが出発する際、老人は、自分が福音記者ヨハネであることを明かし、数年前にエドワード国王が指輪をくれたことを話しました。老人は親切のお礼に6か月後に天国で会うでしょうというメッセージとともに指輪を国王に返してほしいと彼らに託しました。2人の男がイングランドに帰国すると、エドワード国王に指輪とメッセージを渡しました。そして、国王は直ちに自らの死に備えました。国王は6ヵ月後に亡くなり、指輪をはめて埋葬されました。不思議なことに、事実、墓が12世紀に再び開けられたとき、その指輪は完全に保存された遺体の上で見つかりました。

これらの物語の一部は単に伝説であって、本当かもしれませんし、そうではないかもしれません。しかし事実として、クラウン・ジュエルの中で最も有名で世界で一番大きなダイヤモンドは、コー・イ・ヌールとカリナンであると言えるでしょう。

カリナン・ダイヤモンド

カリナンは、1905年1月26日の午後に南アフリカのプレミア鉱山で、鉱山本部長であったキャプテン・フレデリック・ウェルズによって発見されました。それは3106ctの重さ、3 7/8×2 1/4×2 5/8インチで、その日までに発見された他のどのダイヤモンドよりも2倍以上の大きさであったため、当初、彼はこの石がダイヤモンドであることに疑いをもちました。その後、石はトランスバール政府に£150,000で売却されました。そして、2年後には未カットの状態でエドワード7世の66回目の誕生日に贈られました。その規模や価値はわからなかったものの、石のカットは、大きな石をカットする経験のあるアムステルダムのI. J.アッシャー・アンド・カンパニーに依頼され、3ヵ月検討した後、ようやくカリナンはカットされることになりました。

当時、ダイヤモンドを分割する唯一の方法は劈開を利用することでした。―ダイヤモンドの弱い方向に沿って割れるように正確な方向を「打つ」方法ですが、粉砕することを避けるために、慎重に行わなければなりませんでした。そして石を慎重に劈開させた結果、9個の大きな「かけら」と96個の破片になりました。全てのカット工程が終わった後に残った重量は合計1063ctでした。

カリナンⅠ～カリナンⅨと名付けられた9個の大きな石はすべて、ロイヤル・コレクションに属しています。大きい石は、他のジュエリーにも使用できるようにセッティングが作られます。別名「アフリカの星」と呼ばれるカリナンⅠは王笏に用いられ、503ct以上の重さがあります。この石は世界最大の無色のペア・シェイプ・ダイヤモンドです。カリナン II（「アフリカの小さい星」）は、世界最大のクッション・シェイプ・ダイヤモンドで、317ctの重さがあり、帝国王冠の正面にセットされています。この石にもセッティングには2つのプラチナの輪がついており、取り外しが可能です。そしてブローチやペンダントとして単独で着けられ、またカリナン Iと共に着用することもできます。

コー・イ・ヌール・ダイヤモンド

2番目に注目に値するダイヤモンドは、皇太后の王冠にあります。これはコー・イ・ヌールと呼ばれており、「光の山」という意味をもちます。この印象的なダイヤモンドの現在の重量は105.6ctで、もともと186ctあったこの石は、1852年にヴィクトリア女王のためにリカットされました。

この石は、身に着ける女性に幸運をもたらすという伝説があります。しかし、男性には不幸がふりかかります！1739年にペルシャのナーディル・シャーがムガルを征服しましたが、統治者がもつとされるこの珍しい伝説のダイヤモンドを見つけることができませんでした。宮廷の1人が彼にこの石の在り処を話すと、シャーは祝賀会を開き、永遠の友好のしるしとして征服された指導者たちとターバンを交換することを申し出ました。なぜなら、これがコー・イ・ヌールの隠されている場所であったからです。

ダイヤモンドはその後、数十年の間しばしば持ち主が変わりました。1850年までに、コー・イ・ヌールはイングランドへ伝わり、ヴィクトリア女王へわたり、そして現在に至ります。

クラウン・ジュエルは素晴らしいイギリスの歴史がある一方で、伝説に包まれた装飾品以上の存在です。ここには多くの物語と歴史があり、訪れる人々がそれを発見するのを待っています。宝石学的、歴史的な視点でこの宝物を鑑賞するのも良いですし、決して買うことができない宝石を見るのも感動的です。ロンドンで有意義な一日を過ごす方法として、クラウン・ジュエルはお勧めです■ 

この記事はGem-Aの機関誌Gems&Jewellery Sept/Oct 2016 / Volume 25 / No. 5 pp. 14-15から引用したものです。

表紙はカリナン・ダイヤモンドの原石から分割されたカット前の9つの石を大きいものから順に並べたもの。

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The Fascinating History of Antique Turquoise Jewellery

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

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Birthstone Guide: Garnet For Those Born In January

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

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Getting Started with Quartz Inclusions

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

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Understanding Iridescence: Opals, Pearls, Moonstones and Fractured Stones

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

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

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

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Tanzanite: The Contemporary December Birthstone

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

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Birthstone Guide: Turquoise For Those Born In December

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

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Understanding the Cat's Eye Effect in Gemstones

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

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Jade and its Importance in China

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

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Highlights of Gem-A Conference 2019

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

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Having successfully completed her Gemmology Diploma and Diamond Diploma, Charlotte Pittel FGA DGA shares an abridged version of her excellent project on Cardinal Jules Mazarin and his legendary love of diamonds.

The Mazarin diamonds were a collection of 18 diamonds left to Louis XIV and the French Crown Jewels by Cardinal Jules Mazarin. Discovering the story of this group of diamonds, the man who collected them and what happened to them is like an incredible work of fiction.

The Life of Cardinal Mazarin

Born Giulio Raimondo Mazzarino on July 14, 1602 to a minor Italian noble family, Mazarin was a man of many interests and talents. His early education was at Jesuit school in Rome before studying law in Madrid. On his return to Rome around 1622 he attended the University of Rome La Sapienza, and following a spiritual awakening he entered the pontifical army.

In 1628 he joined the diplomatic services for the Holy See and became involved in Italian politics whilst working alongside the Cardinals Sachetti and Barberini. His subtlety, patience and hard work were recognised and in 1630, during the war between France and Spain over Mantua, he was sent to negotiate with Cardinal Richelieu.

Richelieu, impressed with the young man, invited him to Paris where he soon became a confidant and advisor to the Cardinal, joining the court of Louis XIII and Queen Anne d’Autriche. After taking French citizenship he became known as Jules Mazarin and in 1641, was promoted to the rank of Cardinal.

Following Richelieu’s death in 1642, Mazarin succeeded him as the Chief Minister of France and, after the death of Louis XIII in 1643, assisted the Regent Queen Anne in governing France on behalf of her then child son, Louis XIV.

Mazarin was a keen student of the arts, but diamonds were his first love. His collection contained the most beautiful examples, many of them sourced from other European royal families, his preferred jewellers of the time including Lescot, Gabouri, Lopés, and almost certainly from renowned traveller Jean Baptiste Tavernier (1605-1689), who would also supply King Louis XIV.

The 18 Mazarin Diamonds. Illustration inspired by the work of author, Bernard Morel. Image: Charlotte Pittel.

Following his death, Mazarin made generous donations to hospitals, hostels and the arts, and bequeathed his extensive collections of jewellery and gems. Queen Anne received the Rose d’Angleterre (a large round diamond of approximately 14 carats) and a perfect cabochon ruby in a ring.

The Duc d’Orléans received 31 emeralds, while Queen Marie-Thérese was bequeathed a cluster of diamonds. Among his more noteworthy instructions, however, was his wish that a collection of 18 diamonds be given to the King and the Crown of France, on condition that they carry the name Mazarin.

The Famous Mazarin Diamonds

Mazarin assembled this rare and beautiful collection of 18 stones towards the end of his life. Only three of these stones are named: the Sancy, the Mirror of Portugal and the Grand Mazarin. Sadly, due to the tumultuous nature of 18th century French history, many of the 18 stones have disappeared.

The Mazarin I — the Sancy Diamond

It is believed that the 106 (old) carat Sancy formed part of the collection of Charles the Bold, Duke of Burgundy. Following his death it disappeared for over 20 years, finally reappearing in Germany in the hands of a merchant banker named Jacob Fugger. He planned to sell the diamond to the King of Portugal, Don Manuel I, and re-cut it into the pear shape we see today.

During a period of huge political upheaval and conflict between England, France, Spain and Portugal, the diamond would finally end up in the collection (and take the name) of Nicholas de Harley, Seigneur de Sancy and Baron de Maule (1546-1629).

De Sancy was made Superintendent of France by Henry IV and pledged his diamonds to raise money for the crown. In 1596, however, he negotiated the sale of the stone to James I of England, who set the Sancy as a pendant into the jewel known as the Mirror of Great Britain.

Read more: Diamond for Those Born in April

James’s successor Charles I sold off precious stones to raise funds for the Royalist cause and, in 1644, sent his consort Queen Henrietta Maria to France to secure supplies and munitions. She borrowed enormous sums from the Duke of Epernon and pledged the Sancy as collateral. In 1649, when Charles I was beheaded, the Queen was exiled. The Sancy diamond was claimed by the Duke and subsequently sold to Cardinal Mazarin.

The Sancy then became part of the French Crown jewels and was mounted in Louis XV’s coronation crown in 1722. Today, the Sancy is on display at the Louvre Museum in Paris.

The Mazarin II Diamond

Author Bernard Morel suggests that this stone could well be the Pinder diamond, based on a 17th century description and drawings made by Thomas Cletscher. Sir Paul Pinder was a businessman and diplomat and, in 1611, James I made him an ambassador to Turkey where he managed to acquire some exceptional jewels, including the Pindar.

Called at this time the Great Diamond, it was acquired by Charles I in 1625 for 18,000 livres but not paid for. It is likely that this is one of the stones pledged by Queen Henrietta Maria in 1646 and then acquired by Mazarin, becoming known as the Second Mazarin.

It was included in a diamond chain worn by Louis XIV, before being re-cut and set into the centre of the Order of the Golden Fleece made by Jacquemin for Louis XV. Thereafter it was unset and remained in the collection of Louis XVIII until his death in 1824, at which time it was returned to the Crown collection. Sadly, the stone was stolen during the 1848 revolution.

The Mazarin III — the Mirror of Portugal Diamond

This stone belonged to Dom Antonio, Prior of Crato. After a short period with Elizabeth I and named the Portugal Diamond, it was mounted into a pendant set with a large pearl drop and given to Henrietta Maria on her betrothal to Charles I. It eventually became a part of the Mazarin Collection.

Read more: Questions to Ask When Buying a Piece of Gemstone Jewellery

As was the custom, many of the French crown jewels were in settings that allowed a freedom in how they could be worn. As such, the Mirror of Portugal was set not only in Louis XIV’s diamond chain, but also in a hairpin worn by Queen Marie-Thérèse, which also bore the Grand Mazarin and some substantial pearls.

The Third Mazarin was unfortunately lost to the French Crown jewels when a substantial number of the jewels were sent to Constantinople never to return, including the Mirror of Portugal and many other Mazarins.

The Mazarin IV Diamond

This stone was first referenced in Bernard Morel’s book as being set into a pair of Girandole earrings created for Queen Marie-Thérèse. It is shown sitting as the top button with the Mazarin V as a drop. Its pair uses other diamonds, including the Mazarin VI as the drop.

An illustration of Queen Marie-Thérèse's girandole earrings, inspired by the work of Bernard Morel, containing some of the Mazarin diamonds. These earrings were documented in the 1691 inventory of the French Crown Jewels and were valued at 500,000 livres. Image: Charlotte Pittel.

The Mazarin V and VI Diamonds

Both the Mazarin V and Mazarin VI were pierced at the top, so were perfectly shaped to be worn as drop earrings. Records suggest that both of these stones were cut by Francisco Ghiot of Antwerp: 1632 for Mazarin VI and Mazarin V in 1636. In a later inventory of 1774, they show up possibly as rings.

The Mazarin VII — Le Grand Mazarin Diamond

This legendary coloured diamond was sold at Christies on the November 14, 2017, achieving a price of CHF 14,375,000 (approximately GBP £10,969,567.60). A GIA certificate (No. 5182785154) and classification letter confirms that this historic light pink, old-mine brilliant-cut diamond is a Type IIa and weighs approximately 19.07ct.

Read more: The Geology of Diamonds

This diamond can be traced back to Indian mines near the Golconda trading centre, but quite how it came to Cardinal Mazarin is unknown. Once the diamonds were passed to Louis XIV and the Crown Jewels collection, it is believed that Queen Marie-Thérèse was the first to wear it.

Following her death in 1683, Louis regained the Grand Mazarin and added it to his legendary chain of diamonds. It was listed in the 1691 inventory as sitting at number five on a chain of 45 diamonds, numbered in descending order of size. It was added to the crown of Louis XV, along with the Sancy.

The Mazarin VIII Diamond

One of the few diamonds to survive a significant sale in 1795, this Mazarin stone sat at either position six or seven on Louis XIV’s diamond chain. The standout piece in which it featured, along with the Grand Mazarin, was the Diamond Diadem of Marie-Louise, Empress of the French from 1810 to 1814. A large diamond parure was ordered soon after the wedding of the Emperor and Empress, along with a coronet, a necklace, pair of bracelets, girandole earrings and a belt. There was also an order for a substantial diadem.

The Mazarin IX Diamond

Originally described as boat-shaped, the term ‘marquise’ was coined during the reign of Louis XV, largely due to a rumour that it matched the lip shape of his mistress, Madame Marquise de Pompadour. This diamond was set as the eighth button on one of Louis XIV’s justacorps (an open-fitted coat).

The Mazarin X — XVI Diamonds

Along with others, these diamonds were also included in the diamond chain belonging to Louis XIV and also in the coronation crown of Louis XV. The Mazarin XII was described as having a red colouration, probably due to the reddish flaw in its girdle.

The Mazarin XVII-XVIII Diamonds

The last two stones of the collection - XVII and XVIII - were virtually identical, with XVIII slightly larger. It seems that these stones were kept as a pair and used as buttons on a coat belonging to Louis XIV. They are most famed for being part of Empress Eugénie's reliquary brooch of 1855, now part of the collection at the Louvre.

The Mazarin Cut

It should be noted that none of the 18 diamonds that Cardinal Mazarin bequeathed to Louis XIV were cut in the ‘Mazarin cut’. Instead, the cuts were as follows:

1. Pear-shape double rose cuts — I (Sancy), V and VI
2. Rectangular table cuts — II (Mirror of Portugal), III, IV
3. Square table cuts — VII (Grand Mazarin), VIII, X, XI, XII, XIII, XV, XVI
4. Heart-shape flat rose cuts — XVII, XVIII
5. Marquise — IX

The fashioning of diamonds in 17^th century Europe was undeveloped. Until the 1400s the natural form of the diamond was used, so an octahedral crystal or other rough was refined and set (known as the ‘point cut’). The table cut was first seen around 1477, marking the first true cut where the octahedron crystal had its top flattened by grinding and sometimes a culet added to the lower point. Varieties of the table cut are the thick table cut, the mirror cut, the tablet and the lasque cut.

After the table cut followed rose-cut stones; a flat backed stone with a domed front. There were a variety of rose-cut styles in use at the beginning of the 15th century and it was considered the most appropriate cut for a flatter, thinner stone. Early brilliant cuts were first seen in the mid- 1600s, leading us back to the diamond-loving Cardinal Mazarin.

Single-cut or eight-cut diamonds had eight facets on the table and eight facets on the pavilion plus a culet. These then evolved into the double, cut with 16 facets on the table and 16 facets on the pavilion plus a culet.

It was in the mid-17th century that the Mazarin cut appeared, cushion-shaped with 34 facets in total: 17 facets on the table and 17 facets on the pavilion, including the culet, plus a girdle. This design of facets greatly increased the diamond’s reflective properties and it showed more fire and brilliance.

Although Mazarin was a devoted diamond collector, it is unlikely that he actually invented the Mazarin cut. However, he was a definite forerunner in the rise of popularity for this style of cutting and it is most likely that the cut was named after him as a tribute.

The complete version of this project, including references, appendices and a bibliography are available upon request. All images and illustrations are supplied by the author unless otherwise stated.

This article was originally published in the Spring 2019 issue of Gems&Jewellery.

Do you share Mazarin's passion for diamonds? Enhance your knowledge with our Diamond Diploma.

これはGem-Aの機関誌「Gems&Jewellery」2018年春号より引用した記事です。Gem-Aのアシスタント・チューター、ベス・ウェスト FGA DGAがダイヤモンドの壮大な旅をたどり、ダイヤモンド特有の強さについてその起源を古代から探ります。

「彼らが棲んでいた深い谷間では、すべてのものが人間より古い存在であり、それらは神秘の歌を静かに口ずさんでいたのだった」
コーマック・マッカーシー著『ザ・ロード』

炭素は宇宙で4番目に豊富な元素であり、生命にとって最も重要なものの一つです。私たちはおよそ18%の炭素で成り立っています。しかしダイヤモンドの場合は、純粋な炭素で形成され、天然に存在する地球上で最も硬い物質となる方法で結合しています。

しかし、この素晴らしい宝石からは、美しさと耐久性のはるか彼方にある、私たちの世界の始まりをささやく声が聞こえます。

ダイヤモンドは何歳？

最も古いダイヤモンドはおよそ35億年前の太古代に形成されたと証明されています。この時点では、惑星はおよそ10億年間のみ存在していたと考えられていました。そして、地表の状態は安定していました。

ダイヤモンドはどのように生成されるか？

地球はいくつかの層から成ります。最も外側の層は地殻と呼ばれ、6km～40kmの深さがあります。そしてさらに大陸で構成される厚い大陸地殻と海洋地殻 ―つまり海底― に分けられます。地殻の下にはマントルがあり、地球全体の10分の8を占め、主に橄欖岩（かんらんがん）という火成岩で構成されています。

マントルの最上部と地殻はリソスフィア（ギリシャ語で「岩石が多い領域」の意味、岩石圏ともいう）と呼ばれます。この部分は堅いものの、マントルの深い部分では岩石が熔融したり冷えたりして、永久に対流の状態にあります。地球の中心では、液体の外核が固体の内核 ―5500°Cの鉄とニッケルでなる中心部― を覆っています。

太古代に地殻は動いて分裂し、その切り離された部分はそれぞれの場所に落ちつきました。古い動かない地殻の部分を「クラトン」と呼びます。それぞれのクラトンの下、最大300キロメートルの深さにリソスフィア・マントル・キールがあります。このキールは深い部分でもおよそ1200°Cであり、対流によって熱を循環させているマントルよりも温度の低い場所です。

およそ40000気圧に相当する圧力があれば、ダイヤモンドの生成が始まります。これは、およそ140kmの深さと同じです。クラトンの下の深いリソスフィア・キールは、対流によって熱を循環している混沌としたマントルから離れているため、ダイヤモンドが成長するのに最適な場所となりました。

ペトラ・ダイヤモンド社の南アフリカ、フィンシュ（Finsch）鉱山。露天掘りとその後に行われるブロック・ケイビング法（トンネルが見える）。
写真： Charles Evans FGA DGA.

炭素はどこから来たのか？

炭素は、原始時代の（地球の出生から存在した）物質から生じた、または海底が大陸地殻に衝突して押し下げられた時にマントルに引き込まれた物質から生じたと考えられています。

炭素は、マントル付近の流体の中でメタン（CH₄）や炭酸塩（CO₃）等の化合物に閉じ込められています。この流体がマントル・キールを通過すると、橄欖（かんらん）岩に反応し、炭素は化合物から離れてダイヤモンドとして結晶します。最も古いダイヤモンドが生成されたのは、キールの深部です。

ダイヤモンドはどのようにして私たちに届いたのか？

ダイヤモンドは、マントルの深部で生じるマグマの力強く激しい噴火によって深部から噴出されるまで、何千万年もの間、恐竜時代（およそ3億年～8000万年前）頃までキールに留まっていました。

3種類のマグマの中でキンバーライトが最も豊富にダイヤモンドを含んでいます。この強力なマグマが噴火によって「パイプ」と呼ばれる円錐形の穴をつくり、地表まで到達します。噴火で上部に運ばれたダイヤモンドは、穴に閉じ込められたマグマの砕屑物の中にとどまるか、あるいは地表で風化され ―何百万年の間、川や氷河の中で長距離を旅します。

地球の深部から私たちが身に着ける指輪までの道のりをたどると、ダイヤモンドの強さがはっきりとわかります。私たちがダイヤモンドの輝きに包まれるとき、この驚くべき旅を思い出してみてください。

この記事はGems&Jewellery Spring 2018/ Volume 27/ No.1  より引用したものです。

表紙：ダイヤモンドの結晶。写真： Pat Daly

かつて、オパールは「縁起が悪い」ことで知られていましたが、近年はジュエリーの中でも需要の多い宝石の1つとなりました。しかし、あるオパールが数千ポンドの価値がある一方で、他のオパールはほんの数ポンドあるいは数ペンスにしかならないのはなぜでしょうか？ここでは、Gem-A Instrumentsのマネージャー、サマンサ・ロイド FGA EGが、オパールの価値を決める要因と、素晴らしい石と平均的な石とを識別するための簡単かつ必須な情報を提供します。

オパールの色

オパールは規則正しく並んだ珪酸球の集合体で格子状の構造をもっています。この珪酸球どうしの間には、シリカ溶液が含まれています。光が珪酸球を通り抜けてシリカ溶液に当たると、その光は回析し、さまざまな虹色の色調が生じます。

遊色は珪酸球のサイズによって左右されます。例えば、球が小さいと青系の色が見え、大きいと橙色と赤色が現れます。格子状の構造が均一であればあるほど、色は濃く見えます。

オパールの種類

一般的に最もよく知られているのは、採掘されたオパールの大部分を占めるライト・オパールでしょう。下地の色は白色から乳白色や明るい灰色で、上部にはさまざまな度合いの遊色が見られます。

オパール本体が透明の場合 ―ライト・クリスタル・オパールとも呼ばれる― 色斑は表面より下の方に見られます。このような石は非常に高い価格になります。暗い地色をもつ ―時に色の輝きを強める― ブラックあるいはダーク・オパールもまたよく知られています。これは、最も稀少で最も価値あるオパールの変種です。

価値の要因

オパールには価値を変える要因がいくつかあります。既に述べたように、ブラック・オパールはライト・オパールに比べて高値が付きます（特にインクのような黒色の地色のものは高いです）。しかし、中程度のブラック・オパールと比較した場合には、素晴らしい品質のライト・オパールの方が高価になることもあります。 

オパールの価値について考えるときは他の要素が平均的であっても、石の明るさと輝きが特に重要です。したがって、多くの色が見られる石でも輝きが鈍いものは、輝きの良い石と同じ価値にならないことがあります。 

透明度についてはすでに少し触れましたが、これも重要な価値の要因です。ライト・オパールが透明で鮮やかな色を示すクリスタル・オパールであればさらに魅力的で好まれます。  

次に、価値を考える上でより複雑なのは色についてです。オパールの「主となる色」はその価値も影響を及ぼします。赤色は最も高値がつき、続いて値段が高い順に橙色、黄色、緑色、青色、インディゴ、菫色となります。しかし先に述べたように、青緑色の輝く石は鈍い輝きの赤色よりも価値があることを覚えておきましょう。

オパールの模様

稀に、オパール内での光の回折によって興味深い模様が生じることがあり、この模様が石の価値を上げます。縞模様、孔雀の羽の形、筆で描いたような幅のある色のきらめきに比べ、「ピンファイア」や小さな点状模様が見られる場合は魅力が劣ります。 

エチオピア VS オーストラリア 

一つのオパールが数千ポンドもする一方で、他が数百ポンドかそれ以下なのはなぜかを尋ねられることがあるかもしれません。その答えは、オパールの起源にあります。オーストラリアはオパールの重要な産地で、世界で最も素晴らしい数々の石を産出します。

重要なのは、この地域で産出したオパールは含水量が低いことです。つまり、乾燥の影響を受けにくく「ひび割れ」―石の耐久性に影響を与えるヘアライン・フラクチャー（細い線の割れ）― を起こしにくいことを意味します。

これとは対照的に、エチオピアはオパールの新しい産地です。しかし、一部の石は非常に含水量が高く、ジュエリーに用いるには心もとなく不適切といえます。 

エチオピア、オーストラリア・オパールの写真撮影は、ハットンガーデンにある宝石のサプライヤー、 Marcus McCallum FGA, のご協力に感謝いたします。

オパールについてさらに知りたい方は、Gem-Aの図書室にAndrew and Damien Cody著「The Opal Story」をお勧めします。

Gem-A会員の方は、ウェブサイトにアクセスしGems&Jewellery Spring 2017 / Volume 26 / No. 1 にて記事全文をご覧いただけます。

表紙はオーストラリア・オパールのサンプル。すべての写真提供：Marcus McCallum.

Delve into the Gem-A Gemstone & Mineral Collection and you will find this fantastic cut tanzanite and rough tanzanite crystal specimen (pictured above). Here, Gem-A gemmology tutor, Charles Bexfield FGA, explores what makes this relatively new gemmological discovery so special. 

Found in 1967 at the foothills of Mount Kilimanjaro, tanzanite is a relatively new stone and is the purplish blue variety of zoisite. Zoisite is a species of gemstones which share the same chemical composition; zoisite’s composition is calcium aluminium silicate with hydroxyl.

Read more: Why Tanzanite is the Birthstone of December

Today, tanzanite can only be found in the Merelani Hills of Tanzania. A year after its initial discovery it was named after the country in which it was found and introduced to the market by Tiffany & Co., who transformed this previously unknown gemstone into a highly fashionable jewel. Testament to this stone’s huge popularity, in 2002 tanzanite became adopted as a new birthstone for December by the American Gem Trade Association (AGTA).

The Natural Availability of Tanzanite

Tanzanite is a relatively abundant gemstone. Based on a study conducted by TanzaniteOne Mining Ltd in 2012, 270 million carats are mined per year, which equates to 54 tonnes. The current projections suggest the mines will continue to produce gem quality material at the same rate for another 23 years, providing they can progressively dig deeper and reach all the potential material remaining.

A pear-cut zoisite alongside a rough zoisite crystal. Image: Gem-A.

Currently, there are four main commercial mines for tanzanite in Tanzania, separated into blocks A, B, C and D. Each block is owned by a different company; the case study above was carried out on block C, which is by far the largest block on the site, being bigger than the other three mines combined.

Tanzanite Colour and Structure

Tanzanite gains its distinctive purplish blue colour from the trace elements of vanadium and chromium present within its structure. Tanzanite shows very strong pleochroism, which is an optical property and a term used by gemmologists to describe different colours seen in the same material when viewed from different directions. The pleochroism in tanzanite is so strong it is visible by just turning the stone and viewing it through different directions without the aid of a dichroscope.

Pleochroism in tanzanite. Image by Pat Daly FGA.

Providing tanzanite has not been heat-treated, it will show three pleochroic colours: red-violet, deep blue and a greenish yellow. However, if heated above circa 400°C to 500°C, the greenish yellow colour is removed or substantially reduced and the bluish colour deepens.

Read more: What Are the Most Important Gemstone Producing Countries?

The vast majority of tanzanite on the market today is heat-treated to enhance its colour and marketability. Indeed, tanzanite has proven to be a favourite of the rich and famous in recent years, with celebrities such as Beyoncé, Sarah Jessica Parker and Penelope Cruz having been pictured wearing the gem. The Duchess of Cambridge has also on many occasions been spotted wearing a matching set of pear-cut tanzanite earrings and necklace. 

A faceted tanzanite displaying the stone’s distinctive purplish blue colour. Image: Gem-A.

Currently there is no known method for creating synthetic tanzanite. But keep an eye out for synthetic forsterite, which can be used as convincing simulant at first glance. Like tanzanite, it is also strongly pleochroic, however the colours seen when viewed in the different directions are vivid blue and purple, which helps to differentiate between the two stones.

The Value of Tanzanite

On average tanzanite is quite an expensive gemstone; specimens weighing one carat or less will reach prices of about £225 to £250 per carat. Most faceted tanzanite seen commercially on the market is below five carats, while faceted stones over 30 carats are more seldom seen.

The average price of good quality, untreated tanzanite over five carats is about £900 to £1,100 per carat, while smaller sizes around two to three carats can achieve prices of between £350 to £580 per carat. With this in mind, prices do vary depending on colour and treatments, as well as on the particular suppliers or retailers from which you choose to purchase.

Read more: What Makes a Gemstone Rare?

Tanzanite crystals are usually prismatic and quite well formed; any crystals over 50 carats are considered large and are usually sold to mineral or crystal collectors rather than being cut. The largest piece of tanzanite rough reported in the press was found in 2005 by TanzaniteOne Mining Ltd, weighing in at 16,839 carats (7.43lbs or 3.37kg) and measuring approximately 21.8cm x 8cm x 7.11cm, making it a hugely impressive specimen. 

An example of a large rough tanzanite crystal. Image by Pat Daly FGA.

However, the largest tanzanite ever sold at auction is the 423.56 Namunyak Tanzanite, which was set into an 18-carat white gold necklace accompanied by 53 carats of diamonds by jewellery designer Kat Florence; the piece fetched over $300,000 USD at a charity sale in 2016 to raise funds for victims of the Nepal earthquake in 2015.

Tanzanite Buying Advice

Before purchasing a piece of tanzanite jewellery it is important to bear in mind that tanzanite measures between 6 to 7 on the Mohs scale and therefore is not a particularly hard stone. As such, tanzanite can be more liable to scratches and damage and consequently may not be the most suitable stone for wearing as an everyday ring.

Read more: Questions to Ask When Buying a Piece of Gemstone Jewellery

If you decide to buy a tanzanite use a 10x loupe to examine the cut, clarity and any presence of chips or cracks. It is also advisable to compare a number of stones to gauge the hue and saturation of colour. By taking these short steps you can better ensure that you will walk away with a good quality tanzanite specimen.

Discover more incredible specimens in the Gem-A Gemstone & Mineral Collection, including sugilite, stibnite and decorative fossils.

Start your gemmology journey today with the Gem-A Gemmology Foundation course or one of our many Short Courses and Workshops. Contact education@gem-a.com to find out more.

Cover image: Rough and polished tanzanites from the Gem-A Collection, photographed by Henry Mesa.