Gem by Gem

Demantoid Garnet

E-mail Print PDF

The demantoid is one of the most brilliant gemstones that exist, yet until recently it was little known except among collectors and gemstone lovers. Strictly speaking it is a green garnet, or rather the star of the green garnets. Not without reason does it bear a name which means 'diamond-like'. The name comes from the Dutch and makes reference to the outstanding quality of this gem, its incomparable brilliance and fire. Some gemstone lovers claim that a demantoid will continue to glow even in the shade.

The demantoid belongs to the large gemstone family of the garnets, and is actually a variety of the garnet mineral andradite. But it is more than that: it is the most expensive kind of garnet and one of the most precious of all gemstones. It is highly esteemed on account of its rarity coupled with that incredible luminosity. For the latter, at least, there is a plausible explanation: the demantoid has an extremely high refraction (refractive index 1.880 to 1.889). Yet its high dispersion is also remarkable, in other words its ability to split the light which comes in through the facets and break it down into all the colours of the rainbow. The demantoid is a master of this, and does it even better than the diamond.

The spectrum of its colours includes many shades of green, from a slightly yellowish green to a brownish green with a golden glow. Particularly precious is a deep emerald green, though this only occurs very rarely indeed. It is not only fine and unusual, but the specimens are also mostly small, large ones being extremely rare. Once cut, only a few stones weigh more than two carats, and most of them hardly exceed one. And even if you come across one set in a piece of jewellery, it is always likely to be a small stone.

Favourite stone of Russia's star jeweller

There have been a good many beautiful gems which appeared like shooting-stars in the fascinating world of gemstones and vanished from the scene again after only a short time. That indeed is probably what would have happened to the demantoid ... if a goatherd had not happened to be going about his business one day in Namibia. But more of that in a moment.

After its discovery in 1868 in Russia's Ural mountains, the demantoid rapidly proceeded to become a much desired gemstone. Comet-like, it scintillated among the finest jeweller's workshops in Paris, New York and St. Petersburg. First and foremost, Russia's star jeweller Carl Fabergé adored it for its tremendous brilliance and loved to incorporate it in his precious objects. But with the chaos of the First World War, the green star began to fade rapidly. Now, it made only rare appearances in the gemstone trade, and when it did so it was mostly incorporated in an item of second-hand jewellery, or among remnant stocks from the places where it had originally been found in the Urals. Occasionally demantoids were found in other parts of the world, for example in the Congo, or in Korea in 1975, but the quality of these stones was such that they were suitable for collectors' use only.

The situation changed quite suddenly in the middle of the 1990s, when a new seam bearing gemstones was discovered in Namibia. Demantoid was among them.

The story of that discovery reads like a thriller. It is set in the southern Damara country near the Spitzkoppe, as the 'Matterhorn of Africa' is also known. The vast, steppe-like country surrenders to the scorching African sun. Far away on the horizon, the 'black mountains' lie blurred in the bluish haze. It's a dry, hard country. Yet for a long, long time it had held an unknown treasure: gemstones! Millions of years before, liquid magma had shot up from the bowels of the Earth and solidified shortly before it reached the surface. In the course of time, the wind and the elements removed the surface strata until finally only the distinctive granite mountain, the Spitzkoppe, was left. And the gemstones, that is. No-one had an inkling of their existence until in December 1996, quite by chance, a wandering goatherd found a number of crystal-like objects which seemed to him worthy of attention. When he had shown them around a bit in a nearby village, the attention of experts was drawn to the find, and they quickly realised what a treasure was being presented to them.

Meanwhile, the Namibian government has issued concessions for gemstone mines. The rare gemstones are carefully quarried by hand from the parent rock. Care is taken to ensure that as little as possible of the precious raw material is lost.

Why the horsetail influences the value of a demantoid

Demantoids from Namibia come in shades from a vivacious light green to an intense blue-green. They have a striking brilliance. Thanks to their hardness of just under 7 on the Mohs scale, they are well suited to being used in jewellery. However, they do lack one feature by which the true demantoid had always been able to be identified through the microscope: 'horsetail inclusions'. These golden brown crystal threads of chrysotile, mostly appearing to radiate out from the centre of the stone, had previously occurred in almost all demantoids. But - more's the pity - they were missing in the relatively inclusion-free gems from Namibia. These horsetail inclusions were not only typical of the demantoid; they could even increase its value if they were pronounced. That may sound surprising, since as a rule inclusions, which can impair the transparency of a gemstone, are not a welcome sight. But with the demantoid's 'horsetail inclusions' it is a different matter. A beautiful, well formed inclusion can increase the value of the gemstone considerably, a good many collectors being prepared to pay a higher price.

If you are offered a demantoid, it is definitely a good idea to have a look at it through the gemstone microscope. If the stone comes from Russia, you may be able to see these fine, fibrous wisps whose resemblance to the tail of a horse is unmistakable. If that is the case, you have a definite pointer to its origin. At the same time, this 'fingerprint of Nature' shows you that you are holding one of the rarest and most valuable gemstones in your hand. This rarity will also make itself felt in the price, since a demantoid from Russia will be valued much more highly than a green garnet from Namibia, however brilliant the latter may be.


Tsavorite Garnet

E-mail Print PDF

The shining green tsavorite is a young gemstone with a very long geological history. Its home is the East-African bushland along the border between Kenya and Tanzania. The few mines lie in a uniquely beautiful landscape of arid grassland with bare, dry hills. It's dangerous country, the habitat of snakes, and now and then a lion patrols, on the lookout for prey. There, near the world-famous Tsavo National Park, that history began.

In 1967 a British geologist by the name of Campbell R. Bridges was looking for gemstones in the mountains in the north-east of Tanzania. Suddenly he came across some strange, potato-like nodules of rock. It was like a fairy-tale: inside these strange objects he found some beautiful green grains and crystal fragments. A gemmological examination revealed that what he had discovered was green grossularite, a mineral belonging to the colourful gemstone group of the garnets, and one which had only been found on rare occasions until then. It was of an extraordinarily beautiful colour and good transparency. The find made the specialists sit up and take notice; Tiffany & Co. in New York also soon showed an interest in the newly discovered green jewel. However, in spite of all efforts, it was not, at the time, possible to export the stones from Tanzania. But Campbell Bridges was not one to give up easily. As a geologist, he knew that earth strata bearing gemstones were not necessarily limited to one particular area, indeed that they could extend over much greater areas - and in his opinion the stratum he had found was just such a one. For the rock belt in which most of East Africa's gemstone mines lie is very ancient. It began to form many millions of years ago, while the continents were still very much on the move. At that time, the area concerned had actually been under the sea. The sedimental deposits between the continents were greatly compressed and folded as a result of the movement of the massifs. Through tremendous pressure and at high temperatures, the rocks which had been present originally were transformed. New, exciting, beautiful gemstones came into being - among them the tsavorite. Having said that, the tremendous forces of Nature damaged most of the crystals so badly at the time of their formation that today it is usually only grains or fragments which are found.

Campbell B. Bridges persevered. His surmise that the seam bearing the gemstones might possibly continue into Kenya finally put him on the right track. In 1971, he discovered the brilliant green gemstone for the second time, in Kenya. There, he was able to have the find registered officially and begin with the exploitation of the deposit. It was an adventurous business. To protect himself from wild animals, Bridges began by living in a tree-house. In order not to have any of the gemstones stolen, he set a python to watch over them, making use of the fact that his workers were afraid of snakes. It was a wonderful find. Unfortunately, the gemstone had been known only to specialists up to that point in time, but that changed quickly in 1974, when the Tiffany company began a broad promotion campaign which soon made the tsavorite well known in the USA. Further promotion campaigns followed in other countries, and soon the tsavorite was also known at international level.

Green like a garnet ...

So why is the stone called a tsavorite or tsavolite when it is actually a green grossularite and comes from the colourful gemstone family of the Garnet? The nomenclature of gemstones follows certain rules. According to modern mineralogical methods, gemstones are given a name which ends in 'ite'. In honour of the Tsavo National Park, with its abundance of game, and the Tsavo River which flows through it, the former president of Tiffany & Co. Henry Platt, who had followed the developments of the gemstone from the very beginning, proposed the name 'tsavorite'. Sometimes the term 'tsavolite' is used. However, both names denote the same stone, the latter version simply having the Greek suffix '-lite' (stone).

What is it that makes the tsavorite so desirable? Well, for one thing there is its vivid, radiant green. The colour range of the tsavorite includes a springlike light green, an intense blue-green and a deep forest green - colours which have a refreshing and invigorating effect on the senses. However, this gemstone is also valuable on account of its great brilliance. It has, like all the other garnets, a particularly high refractive index (1.734/44). Not without reason did they use to say in the old legends that a garnet was a difficult thing to hide. Its sparkling light was said to remain visible even through clothing.

Unlike many other gemstones, the tsavorite is neither burnt nor oiled. This gemstone is not in need of any such treatment. Like all the other garnets it is simply a piece of pure, unadulterated Nature. Another positive characteristic is its robustness. It has almost the same hardness as the (considerably more expensive) emerald, - approximately 7.5 on the Mohs scale - but it is markedly less sensitive. That is an important feature not only when it comes to the stone's being set but also in its being worn. A tsavorite is not so likely to crack or splinter as a result of an incautious movement. It is well suited to the popular 'invisible setting', in which the stones are set close by one another, a technique which ought not to be used with the more sensitive emerald. Thanks to its great brilliance, the tsavorite is, in this respect, a partner to match the classics: diamond, ruby and sapphire.

Only in rare individual cases is a raw crystal of over 5 carats found, so a cut tsavorite of more than two carats is a rare and precious thing. But then that is one of the special features of this gemstone: that it can display its great luminosity even in small sizes.

There's something very special about this young gemstone with the very long history. With its fresh, vivid green, its good wearing qualities, great brilliance and relatively reasonable prices, it is surely one of the most convincing and honest gemstones that exist.



E-mail Print PDF

Aren't garnets those wonderful deep-red gemstones you often find in antique jewellery? Well yes, to a certain extent, a deep, warm red indeed being the colour most frequently found in garnets. Sadly, however, far too few people are aware that the world of the garnets is far more colourful than that. Spectacular finds, especially in Africa, have enhanced the traditional image of the garnet with a surprising number of hues - even if red does continue to be its principal colour. Thanks to their rich colour spectrum, garnets today can quite happily keep pace with changes of style and the colour trends of fashion. And thanks to the new finds, there is a reliable supply of them too. So in fact this gemstone group in particular is one which gives new impetus to the world of jewellery today.

By the term 'garnet', the specialist understands a group of more than ten different gemstones of similar chemical composition. It is true to say that red is the colour most often encountered, but the garnet also exists in various shades of green, a tender to intense yellow, a fiery orange and some fine earth-coloured nuances. The only colour it cannot offer is blue. Garnets are much sought-after and much worked gemstones - the more so because today it is not only the classical gemstone colours red and green which are so highly esteemed, but also the fine hues in between. Furthermore, the world of the garnets is also rich in rarities such as star garnets and stones whose colour changes depending on whether they are seen in daylight or artificial light.

And what else is there that distinguishes this gemstone group from the others? Well, first of all there is its good hardness of 7 to 7.5 on the Mohs scale. With a few minor exceptions it applies to all the members of the garnet group, and it is the reason for the excellent wearing qualities of these gemstones. Garnets are relatively insensitive and uncomplicated to work with. The only thing they really don't like is being knocked about or subjected to improper heat treatment. A further plus is their high refractive index, the cause of the garnet's great brilliance. The shape of the raw crystals is also interesting. Garnet means something like 'the grainy one', coming from the Latin 'granum', for grain. This makes reference not only to the typical roundish shape of the crystals, but also to the colour of the red garnet, which often puts one in mind of the seeds of a ripe pomegranate. In the Middle Ages, the red garnet was also called the 'carbuncle stone'. And even today, fantasy names like Arizona ruby, Arizona spinel, Montana ruby or New Mexico ruby are still rife in the trade.

The warm red of the garnet illuminated Noah's Ark

Garnets have been known to Man for thousands of years. Noah, it is said, used a garnet lantern to help him steer his ark through the dark night. Garnets are also found in jewellery from early Egyptian, Greek and Roman times. Many an early explorer and traveller liked to carry a garnet with him, for the garnet was popular as a talisman and protective stone, as it was believed to light up the night and protect its bearer from evil and disaster. Today, science has taught us that the garnet's proverbial luminosity comes from its high refractive index.

Not only do garnets have many colours; they also have many names: almandine, andradite, demantoid, grossularite, hessonite, pyrope, rhodolite, tsavorite, spessartine, and uvarovite, to quote but a few. But let us restrict ourselves to the most important and begin with the red garnets. First, there is the fiery red pyrope. Its spirited red, often with a slight brownish nuance, was a gemstone colour much in demand in the 18th and 19th centuries. Garnets from a find in the north-eastern part of the former kingdom of Bohemia - small stones of a wonderful hue - were world-famous at that time. In Europe, they were worked into jewellery a good deal, especially in the Victorian period. That genuine Bohemian garnet jewellery was traditionally set with a large number of small stones, which were close to one another like the seeds of a pomegranate, with their red sparkle. And today too, garnets are still found in former Czechoslovakia and set close together according to the old tradition, the attractiveness of classical garnet jewellery thus consisting mainly in the beauty of the gemstones.

The larger central stones of the typical 'rosettes' are also mostly of garnet, though they belong to a different category. For the 'almandines', named after Alabanda, an ancient city, have a chemical composition that differs somewhat from that of the pyrope. And why, one might ask, are they used as central stones? That's quite simple: because Nature has created the pyrope almost exclusively in small sizes, whilst allowing the almandine to grow in rather larger crystals.

A further garnet variety, also red, is the rhodolite. a mixed crystal of almandine and pyrope. This popular garnet is of a magnificent velvety red with a fine violet or raspberry-red undertone. Originally found in the USA, it now comes mainly from the gemstone mines in East Africa, India and Sri Lanka.

The colourful world of the garnets

The specialist world was amazed a few years ago by the fantastic find of a type of garnet which had been very scarce until then. At the Kunene River, on the border between Namibia and Angola, a deposit of radiant orange to red 'spessartites' was discovered. The spessartite was originally named after the site of a find made in Germany. Spessartites had led a quiet, shadowy existence as stones for gemstone lovers and collectors until that momentous discovery in Namibia. There were hardly any used in jewellery because they were so very rare. But this new find changed the gemstone world. Since then, its wealth has increased by the addition of this unusually fine, intensely radiant orange-red gemstone. Under the trade name 'mandarine-garnet', this wonderfully orange noble garnet became world-famous in no time at all. Unfortunately, the mine in the quiet hills of Namibia was only able to be exploited for a few years. The search for gemstones in the remote bush country began to involve too much effort and became too expensive. So fears grew that this highly precious gemstone, which had shot into the firmament of the gemmological world like a rocket, might only become available in rare individual cases from the stocks of a few cutting-centres. That is, until another deposit of the orange treasures was discovered, this time in Nigeria. Their colour and brilliance are so similar to those of the mandarin garnets from Namibia that only an experienced specialist can discern the subtle differences.

Now for the green garnets. Green garnets?! Is there really such a thing? Indeed there is! In fact, several green varieties are known. First there is 'grossularite', created by Nature in many fine tones of yellow, green and brown and esteemed for its many fine interim hues and earth colours. Here too, there was a spectacular find: in the final year of the 20th century, extensive grossularite deposits were discovered in Mali. These Mali garnets captivate us with their great brilliance. Even the brown, which is otherwise not terribly popular, seems vivid and natural, and goes particularly well with ethnologically inspired trends.

Probably the best known green garnet is the tsavorite or tsavolite, which also belongs to the grossularite group. Tiffany's in New York gave this name to the previous emerald-green stone which was discovered in 1967 by a British geologist, Campbell R. Bridges, in the north-east of Tanzania - after the place where the discovery was made, near the Tsavo National Park with its wealth of game. The green of the tsavorite runs from vivid and light to deep and velvety and, like all garnets, it has particularly good brilliance.

The star of green garnets is the rare demantoid, a gemstone for connoisseurs and gemstone lovers. Its brilliance is positively tremendous, even greater than that of the diamond. Russia's star jeweller Carl Fabergé loved the brilliant green garnet from the Urals more than anything else, and used it in his creations. Meanwhile, the demantoid is no longer quite as scarce in the gemstone trade, thanks to some new finds in Namibia. Demantoids from Namibia are of good colour and brilliance, but they lack one tiny feature: the so-called 'horse-tail inclusions'. These fine, bushy inclusions are the unmistakable, typical feature by which a Russian demantoid is recognised.

Gemstones for every fashion trend

Anyone who loves what is pure and natural and the warm, sun-bathed colours of late summer will be fired with enthusiasm by the colour spectrum of the garnet. Today, garnets mostly come from African countries, but also from India, Russia and Central and South America. The skilled hands of cutters the world over work them into many classical shapes, but also increasingly into modern, imaginative designer cuts. Garnets remain convincing with their natural, unadulterated beauty, the variety of their colours and their tremendous brilliance. Anyone acquiring garnet jewellery can be assured that the joy he or she derives from this beautiful gemstone gift from Nature will be long-lasting and undimmed.




E-mail Print PDF

Spinning purple into gold

Do you love both the purple of amethyst and the sunny gold of citrine? Are you an avid Minnesota Vikings fan? I have the perfect gem for you! Sometimes amethyst and citrine colours are found in the same crystal of quartz. These bicolour yellow and purple quartz gemstones are called ametrine.

With ametrine, you can have both gem colours for the price of one! Ametrine is especially inexpensive when you consider that it comes from only one mine in the world.

The Anahi Mine in Bolivia is the major world producer of ametrine. The mine first became famous in the seventeenth century when a Spanish conquistador received it as a dowry on marrying a princess named Anahi from the Ayoreos tribe. Ametrine was introduced to Europe through the conquistador's gifts to the Spanish queen.

Ametrine is most typically faceted in a rectangular shape with a 50/50 pairing of amethyst and citrine. Sometimes a checkerboard pattern of facets is added to the top to increase light reflection. Ametrine can also be cut to blend the two colours so that the result is a mixture of yellow, purple, and peach tones throughout the stone. Ametrine is also popular among artistic cutters and carvers, who play with the colours, creating landscapes in the stone.

Ametrine is a very durable gemstone suited to a variety of jewellery uses. Most sizes and shapes are available but the colour contrast is most pronounced in sizes of over seven carats.

So why compromise, when you can have two varieties of quartz for the price of one?



E-mail Print PDF

Let's suppose that someone has bought a moped, yet his friends and acquaintances keep talking about his 'wonderful racing machine'. He surely feels confused, or feels that they are taking the mickey out of him. A moped was exactly what he wanted for short trips in good weather, but even the salesman said that he was now in possession of a 'real flyer'.

That's roughly how things go with the citrine, the stone for the month of November. Many people have come to know and love this stone under the name gold topaz, or Madeira or Spanish topaz, although in actual fact it has very little in common with the higher-quality gemstone topaz - except for a few nuances of colour. Thus the history of the citrine is closely interwoven with that of the topaz, and coincides with it completely when it comes to the interpretation of alleged miraculous powers. However, the citrine is a member of the large quartz family, a family which, with its multitude of colours and very various structures, offers gemstone lovers almost everything their hearts desire in terms of adornment and decoration, from absolutely clear rock crystal to black onyx. And it does so at prices which are by no means unaffordable.

The name is derived from the colour - the yellow of the lemon - , although the most sought-after stones have a clear, radiant yellowish to brownish red. Like all crystal quartzes, the citrine has a hardness of 7 on the Mohs scale and is thus, to a large extent, insensitive to scratches. It won't immediately take offence at being knocked about either, since its cleavage properties are non-existent. Even if their refractive index is relatively low, the yellow stones have just that mellow, warm tone that seems to have captured the last glow of autumn. Like golden Rhine wine or sparkling Madeira, heavy and sweet, citrine jewellery shimmers and brings a hint of sunshine to those dull November days.

There are not many yellow gemstones in the world of jewels. A diamond or a sapphire may be yellow - those will be expensive -, or sometimes a tourmaline or chrysoberyl, though these tend toward green somewhat, a golden beryl or eben a pure topaz, which we will mention again later on. However, the citrine fulfils everyone's colour wishes, from lemon yellow to reddish brown.

Rare though it is, yellow does in fact occur in quartz in Nature, if seldom, when there are traces of iron in the silicon dioxide. Historically, it has been found in Spain, on the Scottish island of Arran, in France, Hungary and in several mines overseas. Perhaps the citrine wouldn't have been talked about any more at all if, in the middle of the 18th century, it had not been for the discovery that amethysts and smoky quartzes can also be rendered yellow by so-called burning. This heat treatment at temperatures of between 470 and 560 degrees has to be carried out very carefully and requires a great deal of experience. However, in the course of 200 years, its application has become so much a matter of course that most of the stones available in the trade today are in fact burnt amethysts or smoky quartzes. Only a trained specialist can recognise the signs of heat treatment at all, burnt stones having subtle stripes whilst the yellow of natural ones is cloudy.

In Europe, the boom on these yellow to reddish crystal quartzes didn't begin until, in the 1930s, expatriate agate cutters from Idar-Oberstein sent large quantities of citrine back home, along with amethyst and agate, from Brazil and Uruguay. Thus the golden-yellow quartzes made a contribution to Idar-Oberstein's becoming - and remaining - one of the world's great gemstone centres. Just as they had been used to doing with agate and other kinds of quartz, the cutters faceted the citrine using large, rotating sandstones over decades. The raw stone was actually held in the cutter's hand during this process. If you give that a little thought, it will occur to you just how skilled the cutters from the Hunsrück really were.

The supply of Europe with sufficient raw material came just at the right moment for the nascent upheaval in social conditions. As the bourgeoisie grew in strength, the demand for jewellery across a broader spectrum of social strata also grew, and the citrine found a permanent niche for itself. Since until then it was really only the topaz which was known and used as a gold-coloured gemstone, the yellow and brown crystal quartzes quickly became very popular among the ladies, being known as gold topaz or smoky topaz, or by the double-barrelled names that proclaimed their origin. However, they were also found in step and table cuts as cuff-links and rings in the evening wardrobe of fine gentlemen. At the beginning, perhaps, the notion "it's all on the surface" may have played a part. But there was no other stone to which the wrong name clung as doggedly as the citrine. Even now, jewellery enthusiasts with no specialist knowledge may be astounded when you tell them that their 'gold topaz' is a citrine, in other words not a topaz at all, but quartz.

So what is it that constitutes the difference between the real topaz and the citrine? A fluorine aluminium silicate in chemical terms, the topaz is considerably harder and heavier than quartz, and it has a higher refractive index, which endows it with more fire when the colour is good. It does have one weakness: its good cleavage qualities, which must be taken into account when it is being worked on. It can be found in all the colours of the rainbow and has been known to Man for at least 2000 years. It has not been proved beyond doubt whether the name comes from Sanskrit or Greek, though the Greek name 'topazos' means 'green gemstone'. The Romans dedicated the topaz to Jupiter.

The colour in which the topaz is most commonly found is yellow, and that is the colour in which it occurs in one of the major German gemstone rocks, the Schneckenstein (a topaz-bearing rock said to resemble a snail) in Saxony. In the 18th century, it was mined there during a period of over 60 years. However, most of the crystals were hardly a centimetre in diameter. You had to go to Siberia or Brazil to find crystals as large as your fist. Having said that, anyone who is interested can convince himself of the beauty of cut specimens in the topaz set in Dresden's Grünes Gewölbe (Green Vault). The enormous and magnificent topaz from the Portuguese crown, the Braganza, was for a long time thought to be a diamond.

In mysticism, the topaz is attributed with a cooling, styptic and appetising effect. It is said to dispel sadness, anger and nocturnal fears, to warn its wearer of poisons and protect him or her from sudden death. It is reputed to make men handsome and intelligent and sterile women fertile and happy. However, it is probably better not to rely too much on its magical powers, since it was also claimed that you could immerse your hand in boiling water after a topaz had been thrown into it and retract it again unharmed!

In the Empire style, the topaz was still widespread, but then the more reasonably priced citrine took over from it and even usurped its name. Since then, the topaz has been a rather exotic figure in the jewellery trade, and has been given the additional predicate 'pure' to make it clear that the topaz, not the quartz topaz, is meant. And it is still waiting for its comeback to this day.

Page 8 of 10