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There are no generally accepted definition for the term gem or gemstones, but they all have something special, something beautiful about them. Most gemestones are minerals (e.g., diamond), mineral aggregates (e.g., jade) or more rarely rocks (e.g., lapis lazuli). Some are organic formations (e.g., amber) , and other gem materials are of synthetic origin.
For some gemstones, the source of specialness and beauty is the color, an unusual optical phenomenon, or the shine that makes them stand out in comparison to other stones. For other stones, it is the hardness or an interesting inclusion that makes them special. Rarity also plays a role in the classification as gemestone.
Color: Green or Bluish-green: Daylight; Red, Purplish-red, Raspberry red: Incandescent light
Mohs' Hardness: 8 1/2
Density: 3.70 - 3.78
Chemical Composition:BeAl2O4 Beryllium Aluminum Oxide
Refractive index: 1.746 - 1.763
Transparency: Transparent to Opaque
Alexandrite is a gem variety of the mineral chrysoberyl. Named after the Russian Czar Alexander II (1818-1881), it was discovered only as recently as 1830 in the Urals. Green or bluish-green in daylight, alexandrite turns a soft shade of red, purplish-red or raspberry red in incandescent light. This changing of color is best seen in thick stones. This unique optical characteristic makes it one of the most valuable gemstones of all, especially in fine qualities. Alexandrite displaying the cat's-eye effect is a great rarity. Care must be taken when working with it, as it is sensitive to knocks and color changes are possible with exposure to great heat.
If you really get involved in alexandrite, you will be utterly fascinated by this gem. Maybe you will also feel some of the mysterious magic and lore ascribed to it. It is considered a stone of very good omen. In critical situations it is supposed to strengthen the wearer’s intuition, and thus help him or her find new ways forward in situations where logic will not provide an answer. Alexandrite is also reputed to aid creativity and inspire the imagination.
Fine alexandrite is most often found in period jewelry since newly-mined gems are extremely rare. You'll see fine gems offered at auction with impressive estimates. The deposits in the Urals are worked out. Today it is mined in Sri Lanka and Zimbabwe, and since the end of the 1980s especially in Brazil (Minas Gerais). Deposit are also found in Burma, Madagascar, and Tanzania. The largest stone 1,876 carat, was found in Sri Lanka. The largest cut alexandrite weighs 66 carat; it is in the Smithsonian Institution in Washington, D.C.
Color: Purple, Violet, Pale red-violet
Mohs' Hardness: 7
Chemical Composition: SiO2 Silicon Dioxide
Refractive index: 11.544 - 1.553
Amethyst is the most hightly valued stone in the quartz group. The name means "not drunken" (Greek), as amethyst was worn as an amulet againts drunkenness. Purple has long been considered a royal color, so it is not surprising that amethyst has been so much in demand throughout history. Fine amethysts are featured in the British Crown Jewels and were also a favorite of Catherine the Great and Egyptian royalty. Great thinkers like Leonardo da Vinci believed that amethyst could dissipate evil thoughts and quicken the intelligence.
A large number of further miraculous powers are attributed to the amethyst in all sorts of cultures. It was said to protect crops against tempests and locusts, bring good fortune in war and in the hunt, drive out evil spirits and inspire the intellect. A little study of the works of Pliny will reveal that this gemstone, if worn round the neck on a cord made from dog's hair, affords protection against snakebite. Apart from these powers, gemstone therapists say that the amethyst has a sobering and cleansing effect. Amethyst has also been said to quell excessive stomach acid and, according to Hildegard von Bingen, served to combat insect bites and beautify the skin. But the amethyst not only had a firm niche in medicine; it was also esteemed as a stone of friendship.
Heat treatment between 878-1,382 degrees F (470-750 degrees C) produces light yellow, red-brown, green or colorless varieties. There are some amethysts that lose some color in daylight. The fact that these stones can lose their color makes it obvious that amethyst jewelry should not be worn while sunbathing, in a solarium or in a discotheque with black light. Sudden changes of temperature can also be harmful to the stone. The original color can be restores by X-ray radiation. The coloring agent is iron. In artificial light, amethyst does not display as desirable qualities.
The most important deposits are in Brazil ("Palmeira" amethyst of Rio Grande do Sul, "Maraba" amethyst of Para), Madagascar, Zamibia, Uruguay, as well as in Burma (Myanmar), India, Canada, Mexico, Naminia, Russia, Sri Lanka, and the United States (Arizona). The best stones are faceted; others are tumbled or worked into ornaments. Can be confused with precious beryl, flourite, kunzite, spinel, topaz, tourmaline, and tinted glass. Synthetic amethyst is abundant on the gemstone market.
Color: Light blue to Dark blue, blue-green
Mohs' Hardness: 7 1/2 - 8
Density: 2.68 - 2.74
Chemical Composition: Al2Be3Si6O18 aluminum beryllium silicate
Refractive index: 1.564 - 1.596
Transparency: Transparent to Opaque
Aquamarine (Latin - water of the sea) is so named because of its seawater color. Its light blue arouses feelings of sympathy, trust, harmony and friendship. Good feelings. Feelings which are based on mutuality and which prove their worth in lasting relationships. The blue of aquamarine is a divine, eternal colour, because it is the colour of the sky. Aquamarine was long thought to have a soothing influence on married couples, making it a good anniversary gift.
However, aquamarine blue is also the colour of water with its life-giving force. And aquamarine really does seem to have captured the lucid blue of the oceans. Legend says that Neptune, the King of the Sea, gave aquamarine as gifts to the mermaids, and from then on, it has brought love to all who have owned it.
A dark blue is the most desires color. The coloring agent is iron. Lower qualities are heated to 725 - 850 degrees F (400 - 450 degrees C) to change them to the desired permanent aquamarine blue. Higher heat will lead to discoloration. Care must be taken when making jewelry! Color can also be improved with neutron and gamma irradation, but these changes do not last. Aquamarine is brittle and sensitive to pressure. Inclusions of fine, oriented hollow rods or aligned foreign minerals rarely cause a cat's eye effect or asterism with six-rayed star with vivid sheen.
The most important deposits are in Brazil, spread throughout the country. The well-known deposits in Russia (the Urals) seem to be worked out. Other deposits of some commercial significance are in Australia (Queensland), Burma (Myanmar), China, India, Kenya, Madagascar, Mozambique, Namibia, Nigeria, Zambia, Zimbabwe, and the United States. The host rock is pegmatite and coarse-grained granite as well as their weathered material.
The largest aquamarine of gemstone quality was found in 1910 in Marambaya, Minas Gerais (Brazil). It weighed 243 lbs (110.5 kg), was 18 in (48.5 cm) long and 15 1/2 in (42 cm) in diameter, and was cut into many stones with a total weight of over 100,000 ct. There have been finds weighing a few tons, but these aquamarines are opaque and gray, not suitable for cutting.
The preferred cuts are step (emerald) and brilliant-cut with rectangular or long oval shapes. Turbid stones are cut en cabuchon or are used for necklace beads. Designers call it their favourite gemstone. Again and again they take the world by surprise with a new, modern artistic cut, and when they are breaking new ground, aquamarine is a gem that they particularly like to work with. Without doubt, these creative designer cuts have contributed to the great popularity of this gem. The lucid colour of aquamarine makes it easy to see inclusions. For this reason, aquamarine should always be of the greatest possible transparency.
It can be confused with euclase, kyanite, topaz, tourmaline, zircon, and glass imitations. Synthetic aquamarine can be produced but is uneconomical. The "synthetic aquamarine" sold in the trade is really aquamarine-colored syntheric spinel.
Color: Light yellow to Dark yellow, Gold-brown
Mohs' Hardness: 7
Chemical Composition: SiO2 Silicon Dioxide
Refractive index: 1.544 - 1.553
The name is derived from its lemon yellow color. 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 coloring agent is iron. Natural citrines are rare. Most commercial citrines are heat-treated amethysts or smoky quartzes. Brazilian amethyst turns light yellow at 878 degrees F (470 degrees C) and dark yellow to red-brown at 1,022 - 1,040 degrees F (550 - 560 degrees C). Some smoky quartzes turn intocitrine color already at about 390 degrees F (200 degrees C).
Almost all heat-treated citrines are a reddish tint. The natural citrines are mostly pale yellow. Names for citrine such as Bahia, Medeira, or Rio Grande topaz are improper and no longer accepted in the trade as they are deceptive. On the other hand, when one, for example, speaks of Madeira color and/or Madeira citrine, this is a correct usage; the expert properly connects a certain color with the locality name.
Deposits of natural-colored citrines are found in Brazil, Madagascar, and the United States, as well as in Argentina, Burma (Myanmar), Namibia, Russia, Scotland, and Spain. Well-colored citrines are used as ring stones and pendants; less attractive stones are made into necklaces or ornaments.
Can be confused with many yellow gemstones, especially apatite, golden beryl, orthoclase, topaz, and tourmaline, as well as tinted glass.
Color: Emerald green, green, slightly yellowish-green
Mohs' Hardness: 7 1/2 - 8
Density: 2.67 - 2.78
Chemical Composition: Al2Be3Si6O18 Aluminum Beryllium Silicate
Refractive index: 1.565 - 1.602
Transparency: 1.565 - 1.602
The name emerald derives from Greek smaragdos. It means "green stone" and, in ancient times, referred not only to emeralds but also probably to most green stones. Innumerable fantastic stories have grown up around this magnificent gem. The Incas and Aztecs of South America, where the best emeralds are still found today, regarded the emerald as a holy gemstone. Believed to empower the owner with foresight into the future, emerald is also regarded as an amulet for good fortune. However, probably the oldest known finds were once made near the Red Sea in Egypt.
Emeralds have been held in high esteem since ancient times. For that reason, some of the most famous emeralds are to be seen in museums and collections. The New York Museum of Natural History, for example, has an exhibit in which a cup made of pure emerald which belonged to the Emperor Jehangir is shown next to the "Patricia", one of the largest Colombian emerald crystals, which weighs 632 carats.
Emerald, to many, symbolizes rebirth and the abundance of the life force. The rich green hue brings to mind the regeneration of life in spring and hope of new possibilities. But it has also, for centuries, been the colour of beauty and of constant love. In ancient Rome, green was the colour of Venus, the goddess of beauty and love. And today, this colour still occupies a special position in many cultures and religions. Green, for example, is the holy colour of Islam. Many of the states of the Arab League have green in their flags as a symbol of the unity of their faith. Yet this colour has a high status in the Catholic Church too, where green is regarded as the most natural and the most elemental of the liturgical colours.
Emerald is the most precious stone in the beryl group. Its green is incomparable, and is therefore called "emerald green". The coloring agent for the "real green" is chrome. Beryls that are colored by vanadium ought to be called "green beryl" and not emerald. The color is very stable against light and heat, and only alters at 1,292 - 1,472 degrees F (700 - 800 degrees C). The color distribution is often irregular; a dark slightly bluish green is most desired.
Only the finest specimens are transparent. Often the emerald is clouded by inclusions. These are not necessarily classified as faults, but are evidence as to the genuineness of the stone as compared with synthetic and other imitations. The inclusions are like a fingerprint, giving each emerald a distinct personality and distinguishing them as truly natural gemstones. Fine inclusions, however, do not by any means diminish the high regard in which it is held. The expert refers to these inclusions as jardin (French - garden).
Significant deposits are in Columbia, especially the Muzo mine northwest of Bogota. First mined by native tribes, the Muzo deposit was abandoned and rediscovered in 17th century. The mine yeilds fine-quality stones of a deep green color. Mining, apart from shafts, is mainly by step-form terraces. In Brazil there are various deposits in Bahia, Goias, and Mina Gerais. Stones are lighter than Columbian ones, mostly yellow-green, but they are often free of inclusions. Through deposits newly discovered since the beginning of the 1980s, Brazil has become one of the most important suppliers of emeralds.
Further emerald deposits are in Afganistan, Australia (new South Wales, Western Australia), Ghana, India, Madagascar, Malawi, Mozambique, Namibia, Nigeria, Pakistan, Zambia, Tanzania, and the United States (North Carolina). The emerald mines of Cleopatra (perhaps worked as early as 2000 B.C.), east of Aswan in upper Egypt, are of historical interest only.
Because emerald is so sensitive to knocks, a step cut was developed, the four corners being truncated by facets (so-called emerald cut). Clear, transparent qualities are sometimes brilliant cut. Turbid stones are used only for cabuchons or as beads for necklaces. Occasionally emeralds are worn in the natural form, and sometimes engraved.
Today, many emeralds are enhanced with colourless oils or resins. This is a general trade practice, but it does have the consequence that these green treasures react very sensitively to inappropriate treatment. For example, they cannot be cleaned in an ultrasonic bath. The substances that may have been used by the cutter during his work, or applied subsequently, seal the fine pores in the surface of the gem. Removing them will end up giving the stone a matt appearance. For this reason, emerald rings should always be taken off before the wearer puts his or her hands in water containing cleansing agent.
Data common to all Garnets: Color: White
Mohs' Hardness: 6 1/2 - 7 1/2
Transparency: Transparent to Opaque
Chemical Composition: (SIO4)3 Silicate
This is a group of differently colored minerals with similar crystal structure and related 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.
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.
The main representatives are pyrope, almandite and spessartite (pyralspite series), grossularite, andradite, and uvarovite (ugrandite series). Within the series are also mixed members. The name derives from the Latin for grain because of the rounded crystals and similarity to the red kernals of the pomegranate. Garnet, in the popular sense, is usually understood only as the red "carbuncle stones" pyrope and almandite.
The fiery red pyrope, often with a slight brownish nuance, was a gemstone color 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 jewelry a good deal, especially in the Victorian period. That genuine Bohemian garnet jewelry 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 jewelry thus consisting mainly in the beauty of the gemstones.
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 Spessart (forest), 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 jewelry 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.
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.
Color: Blue, Violet, Brownish
Mohs' Hardness: 7 - 7 1/2
Density: 2.58 - 2.66
Chemical Composition: Mg2Al4Si5O18 Magnesium Aluminum Silicate
Refractive Index: 1.542 - 1.578
Transparency: Transparent to Opaque
Also Called Cordierite and Dichroite.
The legendary Viking mariners used thin pieces of iolite as the world's first polarising filter. Looking through an iolite lens, they were able to determine the exact position of the sun, and navigate their way safely to the New World and back. The property that made iolite so valuable to the Vikings is its extreme pleochroism. Iolite has different colours in different directions in the crystal. A cube cut from iolite will look a more or less violet blue, almost like sapphire, from one side, clear as water from the other, and a honey yellow from on top.
The color of iolite (Greek - Violet) is usually blue. Inclusions of hematite and goethite sometimes cause reddish sheen or aventurescence. It has a greasy vitreous luster. Deposits are found in Burma (Myanmar), Brazil, India, Madagascar, Sri Lanka, and the United States.
In the past, this property led some people to call iolite "water sapphire", though the name is now obsolete.
Color: Green, also all other colors
Mohs' Hardness: 6 1/2 - 7
Density: 3.30 - 3.38
Chemical Composition: NaAlSi2O6 Sodium Aluminum Silicate
Refractive Index: 1.652 - 1.688
Transparency: Opaque, Translucent
The name jade goes back to the time of the Spanish conquest of Central and South America and derives from piedra de ijada, i.e., hip stone, as it was seen as a protection against and cure for kidney diseases. The corresponding Chinese work yu has not been generally accepted.
In 1863 in France, the gemstone, which had been known for 7,000 years, was proved to consist of two separate, distinct minerals, namely jadeite and nephrite. Differentiation between jadeite and nephrite is based on properties, but the term jade is used as a description of both.
In prehistoric times, jade was used in many parts of the world for arms and tools because of its exceptional toughness. Therefore nephrite is sometimes called "axe stone". For over 2,000 years, jade was part of the religious cult in China and mystic figures and other symbols were carved from it. In pre-Columbian Central America, jade was more highly valued than gold. With the Spanish conquest, the high art of jade carving in America came to a sudden end. In China, however, this art was never interrupted. In former times, only nephrite was worked in China, but since about 1750 jadeite impoted from Burma (Myanmar) has also been used.
Jade was used not only for the finest objects and cult figures, but also in grave furnishings for high-ranking members of the imperial family. Today, too, this gem is regarded as a symbol of the good, the beautiful and the precious. It embodies the Confucian virtues of wisdom, justice, compassion, modesty and courage, yet it also symbolises the female-erotic. A visit to the jade market, be it in Hong Kong or Rangoon, or at one of the Hong Kong jade auctions organized by Christie's, can give some idea of the significance this gem has for the people of Asia.
Jadeite and nephrite bear a considerable resemblance to each other in terms of their appearance, their hardness and the properties they exhibit when being processed. Both are tough, since they consist of dense, close-grained, matted aggregates, but they differ from one another in their chemical composition and colours. Nephrite ranges mainly from mid to dark green or grey-green, but it can also be white, yellowish or reddish. Rarer, and somewhat tougher, jadeite displays hues which include green, but also white or pink, and reds, blacks, browns and violets. In both minerals, the way the colour is distributed varies a great deal. Only in the very finest jade is the colour evenly distributed. Both nephrite and jadeite often have veins, blemishes and streaks running through them, though these may not always be regarded as flaws. On the contrary, some of these patterns are considered particularly valuable.
Jade is usually cut into smooth dome shapes called cabochons. Jadeite bangles are also very popular in Asian countries. Beads are also very beautiful and some important jadeite necklaces made during the art deco period have fetched hundreds of thousands of dollars in auctions. Most treasured for its vivid greens, jade also comes in lavender, pink, yellow, and white.
Color: Pink-violet, light violet
Mohs' Hardness: 6 1/2 - 7
Density: 3.15 - 3.21
Chemical Composition: LiAlSi2O6 Lithium Aluminum Silicate
Refractive Index: 1.660 - 1.681
Named after the U.S. minerologist George Fredrick Kunz, who first described this gem in 1902, kunzite was first found in Connecticut, USA. But the first commercially significant deposit was discovered in the Pala region of California, where morganite beryl was also first discovered.
The appeal of this gemstone lies in its clarity and its fine delicate pink nuances which often display a hint of violet. These are delicate, tender hues, feminine and seductive. There are frequently aligned inclusions such as tubes or fractures, and the stone has a vivid vitreous luster. In order to make sure that the fine colour is shown to its full advantage, the cutter must align the raw crystal very precisely during his work. The table facet must be perpendicular to the main axis of the stone. The reason is that depending on the angle from which you look at a kunzite, it can appear violet, pink or even colourless. Some kunzites from finds in Afghanistan display a rich, strong violet, a light violet and a light green depending on the angle of observation. Most kunzites, however, have a fairly light colour. Strongly coloured kunzite is rare and thus correspondingly valuable.
The coloring agent is manganese. Stones are mostly light colored and colors can fade in direct sunlight. Brownish and green-violet type can be improved in color by heating to about 300 degrees F (150 degrees C). Deposits occur in granite pegmatite. The main producer of kunzite is Brazil (Minas Gerais). Other deposits are found in Afghanistan, Burma (Myanmar), Madagascar, Pakistan, and the United States. Can be confused with many pink-colored stones, especially amethyst, morganite, petalite, rose quartz, rubellite, sapphire, and topaz, as well as colored glass.
This gemstone with its fine, delicate pink is not only an ideal precious stone for lovers; it is also popular as a healing stone. Kunzite is said to enhance a person's capacity for devotion and understanding and to bestow inner peace and joie de vivre on its wearer.
Color: Lazur blue, Violet, Greenish-blue
Mohs' Hardness: 5 -6
Density: 2.50 - 3.00
Chemical Composition: (NaCa)8 [(Sio4, S, Cl)2 I (AlSi)4]6 Sodium Calcium Aluminum Silicate
Refractive Index: about 1.50
As Lapis Lazuli (Arabic and Latin - blue stone) is composed of several minerals - in addition to lazurite (25 - 40%), including aguite, calcite, diopside, enstatite, mica, hauynite, hornblende, nosean, sodalite, and/or pyrite - it is considered to be not a mineral but a rock. The variation in composition also causes a wide range in the above data.
The coloring agent is sulfur. In the best-quality speciments, the color is evenly distributed, but in general, it is spotty or striated. In the lapis lazuli from Chile (Chilean lapis) and from Russia, a strongly protruding whitish or gray calcite diminishes the value. Well-distributed fine pyrite is advantageous and is taken to show genuineness. Too much pyrite, on the other hand, causes a dull, greenish tint. Color can be improved through slight heating and dyeing. It has a vitreous and greasy luster.
Lapis Lazuli is sensitive to strong pressure and high temperatures, hot baths, acids and alkalines. Rings should be taken off during household works.
For 6,000 years, the deposit producing the finest material has been in the West Hindu Kush mountains in Afghanistan. Lapis lazuli is present there as an irregular occurence in limestone in different terrain. Russian deposits are at the southwest end of Lake Baikal. The matrix is white dolmitic marble. Chile's deposits are north of Santiago. Other deposits are found in Angola, Burma (Myanmar), Canada, Pakistan, California, and Colorado.
Lapis Lazuli was already used in prehistoric times for jewelry. During the Middle Ages, it was also iused as a pigment to produce ultramarine. Some palaces and churches have wall panels and columns inlaid with lapis lazuli. Today it is used for ring stones and necklaces, as well as sculptures, vases, and other ornamental objects.
It can be confused with azurite, dumortierite, dye howlite, lazulite, sodalite, and glass imitations. In 1954, a synthetic grainy spinel, colored with cobalt oxide, with a good lapis color, made an appearance on the market. Inclusions of thin gold pieces simulated the pyrite. Imitations with lapis lazuli pieces and powder, presed or bound with artificial resin, are also on the market.
Lapis lazuli is regarded by many people around the world as the stone of friendship and truth. The blue stone is said to encourage harmony in relationships and help its wearer to be authentic and give his or her opinion openly.
Color: Colorless, Yellow, Pale Sheen
Mohs' Hardness: 6 - 6 1/2
Density: 2.56 - 2.59
Chemical Composition: KAlSi3O8 Potassium Aluminum Silicate
Refractive Index: 1.518-1.526
The ancient Romans theorized that moonstone, with its unearthly shimmer, was formed from frozen moonlight. This appealing gem variety does shine with a cool lunar light but it is the mineral potassium feldspar of the orthoclase (adularia) species with white shimmer, similar to moonshine (therefore the name), quite terrestrial in origin. The shimmer, which is called schiller or adularescence, is caused by the intergrowth of two different types of feldspar, with different refractive indexes.
The shimmer of light of the moonstone is something very special in the fascinating world of gemstones. Specialists refer to the phenomenon as "adularisation". The cause of it is the lamellar inner construction of the gemstone. Incident light rays are refracted and scattered in the stone. In this way, a unique light effect comes about, and it is this which makes the moonstone so distinctive and so desirable.
This gemstone is surrounded by a good deal of mystique and magic. In many cultures, for example in India, it is regarded as a holy, magical gemstone. Also regarded as a "dream stones" which bring the wearer beautiful visions at night. In Arabic countries, women often wear moonstones sewn out of sight into their garments, for in their cultures the moonstone is a symbol of fertility.
In their uncut state moonstones are rather unprepossessing and afford little idea of what it is that actually constitutes their charm: that mysterious shimmer of light. For that shimmer is not really shown to advantage until the art of the cutter has been brought to bear. Classical moonstones are always cut as cabochons, the most important thing being the correct height of the stone. The cutter must also align the axes of the crystal precisely into the zenith of the stone, for that is the only way in which he will bring about the desired light effect.
Traditionally, the classical moonstones, almost transparent and with their bluish shimmer, come from Sri Lanka. However, they are also found in the USA, Brazil, Australia, Myanmar and Madagascar. Since bluish moonstones of good quality have been becoming more and more of a rarity in recent years, prices have risen sharply.
Can be confused with chalcedony, synthetic spinel, and glass imitations. Other moonstones from the fledspar group are also known.
Color: Pale pink, Soft pink to Violet, Salmon-pink
Mohs' Hardness: 7 1/2 - 8
Density: 2.71 - 2.90
Chemical Composition: Al2Be3Si6O18 Aluminum Berylium Silicate
Refractive Index: 1.562 - 1.602
Transparency: Transparent to Opaque
Morganite was first discovered in California in the early twentieth century. A rich gem find of tourmaline, kunzite, and other gems outside San Diego started a gem rush in the region. Morganite was an exciting new discovery, one that drew the attention of the world's most important gem buyer, George Fredrick Kunz of Tiffany & Co. He decided to name it in honor of his biggest customer, millionaire bank tycoon J.P. Morgan, who was an avid gem collector.
Today this gemestone comes from deposits in Afghanistan, Brazil, China, Madagascar, Mozambique, Namibia, Zimbabwe, and the United States (utah and California).
There are morganites in many fine pink hues. Some are decidedly pink, whilst others tend more to lilac or light violet. Or there may be a hint of orange. Inferior qualities can be improved by heating above 752 degrees F (400degrees C). The colour of morganite always emanates charm, esprit and a touch of tenderness.
The name comes from the Greek word onux , which means fingernail. According to Roman Mythology, Cupid cut the divine fingernails of Venus with an arrowhead while she was sleeping. The fates turned the clippings into stone so that no part of the goddess would ever perish.
The black color of onyx was usually enhanced by man. More than 2,000 years ago, Roman historian Pliny described a traditional technique for darkening onyx that is still in use today. The onyx is soaked in sugar water, then placed in strong acid. After boiling for two hours, the acid eats away the sugar and water, leaving pure black carbon. Today cobalt dye is also used.
In fine jewelry, the black backdrop is often supplied by onyx, a black chalcedony quartz with a fine texture. Some onyx also displays white bands or ribbons against a black background. If the layers are even, this type of onyx can be carved into cameos. Its fine texture also makes it ideal material for today's lapidaries. Onyx was often used as the perfect foil for carved rock crystal or the "drop dead red" of rubies in art deco designs. It is also popular in marcasite jewellery.
Color: All Colors, Partially play-of-colors
Mohs' Hardness: 5 1/2 - 6 1/2
Density: 1.98 - 2.50
Chemical Composition: SiO2nH2O Hydrous Silicon Dioxide
Refractive Index: 1.37 - 1.52
Transparency: Transparent, Opaque
Numerous legends and tales surround this colourful gemstone, which can be traced back in its origins to a time long before our memory, to the ancient dream time of the Australian aborigines. It is reported in their legends that the creator came down to Earth on a rainbow, in order to bring the message of peace to all the humans. And at the very spot, where his foot touched the ground, the stones became alive and started sparkling in all the colours of the rainbow. That was the birth of the Opals.
The name opal is derived from an Indian (Sanskrit) work for "stone". It is divided into three subgroups: the Precious opals, the yellow-red fire opals, and the common opals.
The special characteristic of the precious opals is their play-of-color, a display of rainbow-like hues which (especially in rounded cut forms) changes with the angle of observation. The electron-microscope, using a magnification of 20,000, reveals tiny spheres (as small as 0.001 mm in diameer) of the mineral cristobalite layered in siliceous jelly cause the diffraction and interference pattern.
Opal always contains water (3 to 30%). It can happen that in the course of time, the stone loses water, cracks, and the play-of-color diminishes. This can, at least temporarily, be restores by saturation with oil, epoxy resin, or water. The aging process is avoided when stored in moist absordent cotton wool. Care must be taken during setting. A little heat can evaporate the water. Opal is also sensitive to pressure and knocks as well as being affected by acids and alkalines. Opal is often impregnated with plastic to improve appearance.
Fire opal (named after its orange color) often shows no play-of-color. It is usually milky and turbid. The best qualities are clear and translucnet, which makes them suitable for being faceted. They are also very sensitive to every stress. Common opal is opaque, rarely translucent, and shows no play-of-color.
Up to the end of the 19th century, the andesite lavas in the east of Slovakia supplies the best qualities of opal. Then the Australian deposits were discovered. Famous deposits in New South Wales are at Lightning Ridge and White Cliffs; in South Australia at Coober Pedy and Andamooka. Numerous deposits are also found in Queensland. Most of the 0.04 - 0.08 in (1-2 mm)-thin opal layers are bedded in sandstone. Further deposits are found in Brazil, Guatemala, Honduras, Indonesia, Japan, Mexico, Rusia, Nevada, and Idaho.
Color: White, Pink, Silver-, Cream-, Golden-colored, Green, Blue, Black
Mohs' Hardness: 2 1/2 - 4 1/2
Density: 2.60 - 2.85
Chemical Composition: Calcium Carbonate + Organic Substance + Water
Refractive Index: 1.52 - 1.66, Black: 1.53 - 1.69
Transparency: Translucent to Opaque
Most pearls are products of bivalve mollusks mainly of the oyster type (family Ostreidae). They are built up of mother-of-pearl (nacre), which is mainly calcium carbonate (in the form of aragonite), and an organic horn substance (conchiolin) that binds the microcrystals concentrically around an irritant.
The derivation of the name pearl is uncertain, but it may be from a type of shell (Latin - perna) or from its spherical shape (Latin - sphaerula).
Although the Mohs' hardness is only 2 1/2 - 4 1/2, pearls are extraordinarily compact, and it is very difficult to crush them. The size of pearls varies between a pin head and a pigeon's egg. One of the largest fine pearls ever found (called the Hope Pearl after a former owner) is 2 inches (5 cm) long and weighs 454 ct (1,814 grains = 90.8 grams); it is in the South Kensington Museum in London.
The typical pearly luster is produced by the overlapping platelets of aragonite and film of conchiolin nearer to the pearl surface. This formation also causes the interference of light and the resulting iridescent colors (called orient) that can be observed on the pearl surface. The color of pearl varies with the type of mollusk and the water, and is dependent on the color of the upper conchiolin layer. If the conchiolin is irregularly distributed, the pearl becomes spotty.
Pearls are formed by saltwater oysters (genus Pinctada), some freshwater mussels (Unio), and more rarely by other shellfish. They are formed as a result of an irritant that has intruded between the shell of the mollusk and the mantle or into the interior of the mantle. The outer skin of the mantle - the epithelium - normally forms the shell by secretion of the mother-of-pearl, and also encrusts all foreign bodies within its reach. And such an encrustation will develop into a pearl. If a pearl is formed as a wart-like growth on the inside of the shell, it must be separated from the shell when it is collected. Therefore, its shape is always semi-spherical. It is called blister or shell pearl. In the trade, they sometimes cement these to mother-of-pearl backing to form mabe pearls.
When a foreign body enters the inner part of the mantle - the connective tissue - the mollusk forms a non-attracted, rounded pearl as a type of immunity defense. The epithelial tissue, which has been drawn into the connective tissue together with the foreign body, forms a pearl sac around the intruder and isolates it by secretion of nacre. As we now know, the nacre can also produce a pearl without any foreign body. It is sufficient that a part of the epithelium may for any reason (for instance, an injury from the outside) be drawn into the connective tissue of the mantle.
The pearl is valued according ot shape, color, size, surface conditon, and luster. The most valuable is the spherical shape. Those flattened on one side or half-sphericals are called bouton (French - button) or button pearls; irregular pearls are baroque pearls. Pearls long worn in a necklace take on the shape of a little barrel; one speaks of barrel pearls.
Natural pearls are weighed in grains (1 grain 0.05 g = 0.24 ct or 1/4 carat), and today increasingly in carats. The Japanese weight of momme (= 3.75 g = 18.75 ct) is becoming rarer in European trade circle. Traditionally, natural pearl prices were calculated according to weight. Except in large wholesale transactions, cultured pearls prices are normally quoted with regard to size.
Since conchiolin is an organic substance, it is prone to changes, especially to drying out. This can lead to an "aging" of the pearls, limiting their useful life. At first they become dull, then fissures occur, and finally the beads spall. There is no guarantee possible for the life span of a pearl; on average, one estimates 100 to 150 years. But care can certainly preserve and extend the life of pearls. Extreme dryness is damading; pearls are also sensitive to acids, perspiration, cosmetics, and hair spray. And since pearls have a low hardness,they can be easily scratched. Therefore, wear and store them in such a way that the pearl surface is never in contact with metal or other gemstones.
Color: Yellow-green, Olive-green, Brownish
Mohs' Hardness: 6 1/2 - 7
Density: 3.28 - 3.48
Chemical Composition: (Mg,Fe)2SiO4 Magnesium Iron Silicate
Refractive Index: 1.650 - 1.703
The name probably derives from the Arabic word faridat (gem). The name chrysolite (Greek - gold stone) was formerly applied not only to peridot but also to many similar colored stones. The name commonly used in mineralogy is olivine (because of its olive-green color).
Olivine is a mineral that occurs in the series with the end members forsterite (Mg2SiO4) and fayalite (Fe2SiO4). It has a vitreous and greasy luster, and is not resistant to acids. It tends to burst under great stress; therefore, it is sometimes metal-foiled.
Historically, important deposit was on the Red Sea volcanic island Zabargad (St. John), 188 miles (300 km) east of Aswan, Egypt; it was mined for over 3,500 years but forgotten for many centuries, and rediscovered only around 1900. But in the middle of the 1990s, a sensationally rich deposit of the finest peridots had been found in Pakistan, up on an inhospitable pass at some 4000 metres (13,120 ft). In tough climatic conditions which permitted the gemstones to be mined only during the summer months, the unusually large, fine crystals and fragments were brought down into the valley. These stones were finer than anything that had ever been seen before. And the deposits were so rich that the demand for peridots can, for the present, easily be satisfied.
In order to emphasise the special quality of the peridots from Pakistan, these stones are offered as "Kashmir peridots", following the famous Kashmir sapphires. Creative gemstone cutters have succeeded in cutting some fascinatingly beautiful one-off stones of more than 100 carats from some of the large, fine, clear crystals with their magnificent rich green.
Beautiful material is also found in the serpentine quarries in upper Burma (Myanmar). Other deposits have been found in Australia (Queensland), Brazil (Minas Gerais), China, Kenya, Mexico, Pakistan, Sri Lanka, South Africa, Tanzania, and Arizona. In Europe, deposits are found in Norway, north of Bergen. Peridot was brought to Central Europe by the crusaders in the Middle Ages, and was oftern used for ecclesiastical purposes. It was the most popular stone during the Baroque period.
The peridot is one of the few gemstones which come in one color only. The rich, green colour with the slight tinge of gold is caused by very fine traces of iron. From a chemical point of view, peridot is an iron magnesium silicate. The intensity of the colour depends on the amount of iron actually present. The color itself can vary over all shades of yellowish green and olive, and even to a brownish green.
The peridot is cut in accordance with its crystal shape, mostly faceted or in classical table cuts, or round, antique, as an octahedron or oval. Smaller crystals are cut into standardized series stones, larger ones into imaginative one-offs. Cabochons are made if the material contains more inclusions, for the domed cut brings out the fine silky shine of the inclusions to their best.
Color: Varying Red
Mohs' Hardness: 9
Density: 3.97 - 4.05
Chemical Composition: Al2O3 Aluminum Oxide
Refractive Index: 1.762 - 1.778
Transparency: Transparent to Opaque
Ruby is thus named because of its red color (Latin - ruber). It was not until about 1800 that ruby, as well as sapphire, was recognized as belonging to the corundum species. Before that date, red spinel and the red garnet were also designated as ruby.
The red color varies within each individual deposit, so it is not possible to determine the source area from the color. The designations "Burma ruby" ot "Siam ruby" are therefore strictly erroneous, and refer more to quality than origin. The most desirable color is the so-called "pigeon's blood", pure red with a hint of blue. The distribution of color is often uneven, in striped or spots. The substance that provides the color is chromium, and in the case of brownish tones, iron is present as well. As a rough stone, ruby appears dull and greasy, but, when cut, the luster can approach that of diamond. Heat treatment is commonly used to improve the color.
Ruby is the hardest mineral after diamond. However, the hardness varies in different directions. Ruby has no cleavage, but has certain preferred directions of parting. Because of brittleness, care must ne taken when cutting and setting.
Inclusions are common. They are not always indicative of lower quality, but show the difference between a natural and a synthetic stone. The type of inclusion (minerals, growth structures, canals, or other cavities) often indicates the source area.
Production methods are still as primitive as they were a hundred years ago in many locations. In state-owned mines, on the other hand, the usage of machinery is not exactly the rule, but much more frequent than in private companies. Some state-regulated companies (e.g., Mogok in Burma) lately even work with highly mechanized machinery both above- and underground.
Some of the most important deposits are in Burma (Myanmar), Thailand, Sri Lanka, and Tanzania. For centuries, the most important have been in upper Burma near Mogok. The ruby-bearing layer runs several yards under the surface. Apparently, only about one percent of production is of gem quality. Some of the rubies are of pigeon's blood color. They are considered to be the most valuable rubies of all. In the early 1990s, large new deposits were discovered at Mong Hsu in Myanmar. Rubies from Thailand often have a brown or violet tint to them. They are found southeast of Bangkok in the district of Chantaburi in clayey Gravels. Shafts are sunk to a depth of 26 ft (8 m). However, in recent years, Thai ruby production has been declining.
Rubies from Sri Lanka are usually light red to raspberry-red. Some of the rubies are recovered from the river sands and gravels. Since 1950s, Tanzania has produced a decorative green rock, zoisite (anyolite), with quite large, mostly opaque rubies. Only a few crystals are cuttable, most being used as decorative stones. On the upper Umba River (northwest Tanzania), on the other hand, rubies with gemstone quality have been found that are violet to brown-red.
Ruby is one of the most expensive gems, large rubies being rarer than comparable diamonds. The largest cuttable ruby weighed 400 ct; it was found in Burma and divided into three parts. Famous stones of exceptional beauty are the Edwardes ruby (167 ct) in the British Museum of Natural History in London, the Rosser Reeves star ruby (138.7 ct) in the Smithsonian Institution in Washington D.C., the De Long star ruby (100 ct) in the American Museum of Natural History in New York, and the Peace ruby (43 ct), thus called because it was found in 1919 at the end of World War I.
Color: Blue in various tones, Colorless, Pink, Orange, Yellow, Green, Purple, Black
Mohs' Hardness: 9
Density: 3.95 - 4.03
Chemical Composition: Al2O3 Aluminum Oxide
Refractive Index: 1.762 - 1.788
Transparency: Transparent to Opaque
The name sapphire (Greek - blue) used to be applied to various stones. In antiquity and as late as the Middle Ages, the name sapphire was understood to mean what is today described as lapis lazuli. Around 1800 it was recognized that sapphire and ruby are gem varieties of corundum. At first only the blue variety was called sapphire, and corundums of other colors (with the exeption of red) were given special, misleading names, such as "Oriental peridot" for the green variety of "Oriental topaz" for the yellow type.
Today, corundums of gemstone quality of all colors except red are called sapphire. Red varieties are called rubies. The various colors of sapphire are qualified by description, e.g., green sapphire or yellow sapphire. Colorless sapphire is called leuko-sapphire (Greek - white), pinkish orange sapphire, Padparadscha (sinhalese for "Lotus Flower")
There is no definite demarcation between ruby and sapphire. Light red, pink, or violet corundums are usually called sapphires, as in this way they have individual values in comparison with other colors. If they were grouped as rubies, they would be stones of inferior quality. The coloring agent in blue sapphire are iron and titanium; and in violet stones, vanadium. A small iron content results in yellow and green tones; chromium produces pink, iron and vanadium orange tones. The most desired color is a pure cornflower-blue. In artificial incandescent light, some sapphires can appear to be ink-colored or black-blue. Through heat treatment at temperatures of about 3,100 - 3,300 degrees F (1,700 - 1,800 degrees C), some cloudy sapphires, non distinct in color, can change to a bright blue permanent color.
Its hardness is the same as ruby and also differs cleary in different directions (an important factor in cutting). There is no flourescence characteristics for all sapphires. Inclusions of rutile needles result in a silky shine; oriented, i.e., aligned, needles cause a six-rayed star sapphire.
Host rocks of sapphire are dolomotized limestones, marble, basalt, or pegmatite. It is mined mainly from alluvial deposits or deposits formed by waethering, rarely from the primary rock. Production methods are usually very simple. The underground gem-bearing layers is worked from hand-dug holes and trenches. The separation of clay, sand, and gravel is done by washing out the gemstones due to their higher density. Final selection is made by hand. Sapphire is much more common than ruby, as the substance which lead color to sapphire are more common than those of ruby. Today, economically important saqpphire deposits are in Australia, Burma (Myanmar), Sri Lanka, and Thailand. In 1966, the largest star sapphire was found in Burma near Mogok, a crystal of 63,000 ct (28 lbs / 12.6 kg).
The most desired sapphires used to come from Kashmir (India), where the deposits were situated at a height of 16,500 ft (5,000 m) in the Zaskar mountains. Production varied since 1880, and the deposits have apparently been worked out. The host rock is a kaolin-rich pegmatite in crystalline schist. The decomposition product yields sapphires of deep cornflower-blue color, often with a silky sheen. Most stones sold today as Kashmir sapphire comes from Burma.
There are also significant sapphire deposits in Brazil, Cambodia, China, Kenya, Madagascar, Malawi, Nigeria, Pakistan, Rwanda, Tanzania, Vietnam, and Zimbabwe.
Large sapphires are rare. They are sometimes named in the same way as famous diamonds. The American Museum of Natural History (New York) owns the "Star of India", perhaps the largest cut sapphire (536 ct); also the "Midnight Star", a black star sapphire (116 ct). The "Star of Asia", a star sapphire weighing 330 ct, is owned by the Smithsonian Institution in Washington, D.C. Two famous sapphires (St. Edward's and the Stuart sapphire) are part of the English Crown Jewels. In the United States, the head of presidents Washington, Lincoln, and Eisenhower have been carved out of three large sapphires, each weighing roughly 2,000 ct.
Color: Sapphire blue, Amethyst, Violet
Mohs' Hardness: 6 1/2 - 7
Chemical Composition Ca2Al3(SiO4)3(OH) Calsium Aluminum Silicate
Refractive Index: 1.691 - 1.7000
Tanzanite is named after the East African state of Tanzania, the only place in the world where it has been found. On its discovery in 1967, it was celebrated by the specialists as the "gemstone of the 20th century". Millions of years ago, metamorphic schists, gneisses and quartzites formed impressive, flat-topped inselbergs on a vast plain in the shadow of Kilimanjaro. The precious crystals grew in deposits on the inside of these unusual elevations. For a long, long time they were hidden from the eye of Man, until one day some passing Masai shepherds noticed some sparkling crystals lying in the sun and took them along with them.
It was introduced by the New York jewelers Tiffany & Co., proposed the name "tanzanite", after the place where the stone had been found - a name which quickly came into general use in the trade. And it was Tiffany's who, two years after its discovery, presented the exclusive gemstone to the general public with a broad-based advertising campaign.
The deep blue of the tanzanite is fantastic. In good quality, the color is ultramarine to sapphire blue; in artificual light, it appears more amethyst violet. The most coveted colour is a blue surrounded by a delicate hint of purple, which has a particularly wonderful effect in sizes of over 10 carats. The well developed polychromaticity of the tanzanite is typical: depending on the angle from which you look at it, the stone may appear blue, purple or brownish-yellow. When heated to 752 - 932 degrees F (400 - 500 degrees C), the interfering yellowish and brown tints vanish, and the blue deepens. This burning is a method of treatment which is regarded as customary in the trade, but the raw stones must be as free of inclusions as possible, since otherwise fissures may occur. In fact working with tanzanite can sometimes give even the most experienced cutter a bit of a headache, the cleavage of this gemstone being very pronounced in one direction. This exclusive gemstone is cut in every imaginable shape from the classical round shape to a number of imaginative designer cuts.
Color: Colorless, Yellow, Orange, Red-brown, Light to dark blue, Pink-red, Red, Violet, Light green
Mohs' Hardness: 8
Density: 3.49 - 3.57
Chemical Composition: Al2SiO4 (F,OH)2 Fluor containing Aluminum Silicate
Refractive Index: 1.609 - 1.643
Transparency: Transparent, Translucent
Formerly, the name topaz was not applied consistently or specifically; one called all yellow and golden-brown, and sometimes also green, gemstones topaz. The name topaz is most probably derived from an island in the Red Sea, now Zabargad but formerly Topazos, the ancient source of peridot.
The topaz has been known for at least 2,000 years and is one of the gemstones which form the foundations of the twelve gates to the Holy City of the New Jerusalem. These so-called apocalyptic stones are intended to serve in protection against enemies and as a symbol of beauty and splendor. The Romans also dedicated the topaz to Jupiter
Colors of the gemstone that is today called topaz are rarely vivid. The most common color is yellow with a red tint; most valuable is pink to reddish-orange. The coloring agents are iron and chromium. Some yellowish-brown varieties of certain deposits gradually fade in the sunlight. Care must be taken duting polishing and setting because of the danger of cleavage. They are also not resistant to hot sulphuric acid. The luster is vitreous.
Deposits are associated with pegmatites or secondary placers. During the 18th century, the most famous topaz mine was at Schneckenstein in the southern Voigtland in Saxony. Today, Brazil (Mina Gerais) is the most important supplier. Other deposits are in Afghanistan, Australia, Burma (Myanmar), China, Japan, Madagascar, Mexico, Namibia, Nigeria, Pakistan, Russia (the Urals, Transbaikalia), Zimbabwe, Sri Lanka, and the United States. Light blue topazes are found also in Northern Ireland, Scotland, and Cornwall, England.
Topazes weighing several pounds are known. In 1964 some blue topazes were found in Ukrain, each weighing about 220 lbs (100 kg). The Smithsonian Institution in Wachington, D.C., owns cut topazes of several thousand carats each. Colored stones are usually step-(emerald) or scissor-cut, and colorless ones or weekly colored ones are brilliant-cut. Topazes with disordered inclusions are cut en cabochon.
Since 1976, blue synthetic topazes are known. Almost all blue topaz sold today is produced by first irradiating and then heating natural colorless topaz. Since the quartz variety citrine is in the trade often falsely called "gold topaz" or Madeira topaz", real topaz is sometimes called precious topaz. in order to clearly distinguish them.
Color: Colorless, Pink, Red, Yellow, Brown, Green, Blue, Violet, Black, Multicolor
Mohs' Hardness: 7 - 7 1/2
Density: 2.82 - 3.32
Refractive Index: 1.614 - 1.666
Transparency: Transparent to Opaque
Even though tourmaline has been known since antiquity in the Mediterranean region, the Dutch imported it only in 1703 from Sri Lanka to Western and Central Europe. They gave the new gems a Sinhalese name, Turamali, which is thought to mean "stone with mixed colors". According to an old Egyptian legend, the tourmaline, on its long journey up from the centre of the Earth, passed over a rainbow. In doing so, it assumed all the colours of the rainbow. And that is why it is also referred to as the "gemstone of the rainbow" today.
Unicolor tourmaline crystals are quite rare. Most show varoius tones in the same crystal or even different colors. There are colorless tourmalines with black crystal ends, green ones with red crystal ends, and some with different-colored layers. There are stones whose core is red, the inner layer white, and the outer layers green - called "watermelon". Some tourmalines show a slight change of color in artificial light. they have a vitreous sheen on crystal surfaces, a greasy sheen on fractured surfaces.
By heating ans subsequent cooling, as well as by applying pressure, i.e., by rubbing, a tourmaline crystal will become electrically charged. It will then attract dust particles as well a small pieces of paper (pyro- and piezo-electricity). the Dutch, who first imported tourmaline into Europe, knew of this effect. They used a heated stone to pull ash out of their meerschaum pipes and thus called this strange stone aschentrekker (ash puller). For a long time this was the popular name of the tourmaline. Due to this pyroelectric effect, tourmaline has to be cleaned more often than other gemstones.
Deposits are found in pegmatites and alluvial deposits. The most important tourmaline supplier is Brazil (Mina Gerais, Paraiba). Other deposits are in Afghanistan, Australia, Burma (Myanmar), India, Madagascar, Malawi, Mozambique, Russia, Sri Lanka, Tanzania, the United States (California, Maine), and Zaire. In Europe, there are tourmaline deposits on Elba (Italy) and in Switzerland (Tessin).
The most desired colors are intense pink and green. It is used in different cuts. Because of the strong pleochroism, dark stones must be cut so that the table lies parallel to the main axis. In the case of pale stones, the table should be perpendicular to the long axis in order to obtain a deeper color.
By heating to 842 - 1,202 degrees F (450 - 650 degrees C), color changes can be produced in some tourmalines. Some green tourmalines become emerald green; others are lightened. The color of tourmalines which have been changed with gamma-irradiation may fade. Synthetic tourmalines are used only for research purposes. The stones, offered as synthetic tourmaline, are really tourmaline-colored synthetic spinels.
Color: Sky-blue, Blue-green, Apple-green
Mohs' Hardness: 5 - 6
Density: 2.31 - 2.84
Chemical Composition: CuAl6 (PO4)4(OH)8 4H2O a copper containing basic Aluminum Phosphate
Refractive Index: 1.610 - 1.650
Transparency: Translucent, Opaque
Turquoise is among the oldest known gemstones - it has been mined since 3,200 BC. It graced the necks of Egyptian Pharaohs and adorned the ceremonial dress of early Native Americans. This robin egg blue hued gemstone has been attributed with healing powers, promoting the wearer's status and wealth, protection from evil and brings good luck. The name turquoise means "Turkish stone" because the trade route that brought it to Europe used to come via Turkey.
Pure blue color is rare; mostly turquoise is interspersed with brown, dark gray, or black veins of other minerals or the host rock. Such stones are called turquoise matrix. It can also be intergrown with malachite and chrysocolla. It has a wawy luster or mat. Most of the so-called turquoise found inthe United States contain Fe (substituting for Al) and is thus really a mixture with chalcosiderite. Iron imparts a greenish color.
The popular sky-blue color changes at 482 degrees F (250 degrees C) into a dull green (be careful when soldering). A negative change in color can also be brought about by the influence of light, perspitation, oils, cosmetics, and household detergents, as well as loss of natural water content. Turquoise rings should be removed before hands are washed.
Occurs in dense form, filling in fissures, as grape-like masses or nodules. Thickness of veins up to 0.8 in (20 mm). The best qualities are found in northeast Iran near Nishapur. Additional deposits are found in Afghanistan, Argentina, Australia, Brazil, China, Mexico, Tanzania, and the United States. The deposits in Sinai, Egypt, were already worked out by 2000 B.C. In the early Victorian period, sky-blue turquoise was most popular. Today, it is used en cabochon, for brooches, necklaces, and bracelets, as well as ornamental objects.
Because the stone is so porous, turquoise is often soaked with artificial resin, which improves color and at the same time hardens the surface. The color can also be improved with oil or paraffin, Berliner blue, aniline colors. or copper salt. It is imitated by dyed chalcedony, dyed howlite, powdered turquoise pieces that are baked with a glue mixture, as well as by glass, porcelain, and plastic. Suyn thetic turquoise, with or without matrix, has been on the market with good qualities since about 1970.
Color: Colorless, Yellow, Brown, Orange, Red, Violet, Blue, Green
Mohs' Hardness: 6 1/2 - 7 1/2
Density: 3.93 - 4.73
Chemical Composition: ZrSiO4 Zirconium Silicate
Refractive Index: 1.810 - 2.024
Transparency: Transparent to Translucent
Zircon has been known since antiquity, albeit under various names. Today's name is most likely derived from the Persian language ("golden color"). Zircon was said to aid sleep, bring prosperity, and promote honor and wisdom in its owner.
Because of its high refractive index and strong dispersion, it has great brillance and intensive fire. It is brittle and therefore sensitive to knocks and pressure; the edges are easily damaged. The luster is vitreous to a brilliant sheen. A content of radioactive elements (uranium, thorium) causes large variations of physical properties. Zircons with the highest values in optical properties are designed as high zircons, those with the lowest values as low zircons. In between are the medium zircons. The alteration caused by radioactive elements in green (low) zircons is so advanced that these stones can be nearly amorphous, even though their outer appearance seems unchanged. These green, slightly radioactive zircons are rarely found in the gemstone trade, but are highly prized by collectors.
Deposits are mainly alluvial; found in Burma (Myanmar), Cambodia, Sri Lanka, Thailand, as well as Australia, Brazil, Korea, Madagascar, Mozambique, Nigeria, Tanzania, and Vietnam.
In nature, the gray-brown and red-brown zircons are the most common. Colorless speciemens are rare. In the South Asian countries where it is found, the brown varieties are heat-treated at temperatures of 1,472 - 1,832 degrees F (800 - 1,000 degrees C), producing colorless and blue zircons. These colors do not necessarily remain constant; ultraviolet reays or sunlight can produce changes. Zircon occurs in a wide range of colours, but for many years the most popular was the colourless variety, which looks more like diamond than any other natural stone because of its brilliance and dispersion.
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