Gemology Related Links

Gemstone Varieties

AMBER

Amber, the gold of the Ages.

Amber is one of the oldest gems ever used. Its “warm like the sun rays” color and its low hardness (2-2,5 in the Mohs scale) are responsible for its extensive use since the earlier ages of humanity.

This gem originates from the sticky resin of prehistoric resineous trees which solidified with time in sediments layers. All resins don’t deserve the name of Amber because most of them cannot get that old: 60 to 10 millions years. Furthermore, they may come from other kinds of trees.
Semi-fossil resins that are about 1000 years old or less are called Copal. They have the same gemological properties and inclusions than Amber (refractive index of 1.54 and specific gravity about 1,05-1,10) but are much more sensitive to dissolution in oils and organic liquids like ether, alcohol, benzene. Amber and Copal must not be in contact with these substances or the skin to preserve its polish and shape. The better way to clean them is water with soap.

Amber is much appraised for the type of inclusions it displays: Gemstones are the witnesses of the Earth’s history; Amber is the only one which witnesses Life’s history too.
Insects within Amber are millions of years old and perfectly kept intact. Prehistoric flies, ants, spiders, leaves and pieces of wood within amber are the best clues to study the prehuman and prehistoric fauna.
Pieces of Amber with the right inclusions are very valuable and researched by collectors and entomologists.

In the times of early Greeks and Romans, it was called Elektron or Electrum due to its capacity to produce static electricity when vigorously rubbed. This old name would lead to the word: electricity. It was also considered as a talisman against evils and headaches, as a small part of the sun. At that time only nobility and gladiators were allowed to wear it.

Among the multiple hues Amber can have, the most common and most appreciated are the transparent yellow-orange hues. But it can also exist, very rarely, in red (Sicily, Romania:
Roumianite variety, Burma: Burmierite), blue (deposit of Polo Quemado in Saint Domingue), green (Sicily) and white (bone-like amber).

The oldest and most renowned deposit is the Baltic Sea, from Germany to Russia, with a special concentration in the Kaliningrad area ( the Russian enclave in Poland also known as K?nisgberg). Other deposits of valuable ambers are mainly: Dominican Republic (renowned for its insects and plants inclusions), Burma, (specific red hue, highest hardness: 3 in the Mohs scale), Thailand, Canada, Mexico, etc.

Like many gemstones, Amber is subject to imitation and treatments. Its most common imitations are plastic or resin, which have close gemological and optical properties to those of Amber. However it is easy to differentiate with the hot point testing method: the resineous smelling of Amber is easily recognizable from the acrid one of plastics. On the other hand, due to its low melting point small pieces of amber can be pressed and fused together to get a bigger piece, a treatment which is easily recognizable with a 10X loupe and known as “pressed Amber”.

From the earlier ages of humanity to nowadays, amber is still a mysterious and precious gem, the only one which never is cold when touched.

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APATITE

Apatite name is coming from a greek word "apate" meaning "to deceit" as it is a gemstone that can easily confuse because of the color shown by some specimens that turn from blue to green when we move the stone! Apatite can also possibly be mistaken with other gemstones and especially tourmaline.
Apatite with a hardness of 5 on the Moh's scale of hardness is a rather soft stone. This characteristic along with the fact that it is a brittle stone make it of limited use in jewelry as these stone often break when the jeweler try to set them. Cutting and setting apatites is a real challenge! Apatite is also sensitive to acids.
This beautiful stone occurs in many colors: blue, green, pink, red, yellow, violet and colorless. The blue and green shades can make such exceptional stones that once you see them, you will never forget them. Stones can be transparent to opaque. The blue Burmese apatite is often "dichroic" which means that it can appear to be two different colors: Blue and green depending on which way you look at the stone. In other colors this particularity is less apparent. Apatite fashioned as a cut gemstone is very popular with collectors, It sometimes show a cat's eye effect, a ray of light running through the center of the stone resembling a cat's eye.

Apatite is a basic fluoro and chloro calcium phosphate: Ca5(PO4)(F,OH,Cl) that crystallize in the hexagonal system. Blue apatite owns its color to manganese, pink to color center (these apatites traditionally from Mexico see their color fading with exposition to sun) and other colors to rare earth elements. Apatite is an abundant material that occurs in many different types of rocks: Marbles, pegmatites, ore veins in many areas of the world.
In addition to Mogok in Burma, it is also mined mainly in Sri Lanka, Brazil, Mexico and also: Russia, Africa, Sweden, Spain, Canada and Mexico. As with most gemstones, the color of the stones will vary with locality.

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AQUAMARINE and BERYLS

Aquamarine is a member of the beryl family, a group of gemstones including:

Emerald: Chromium and vanadium colored green beryl.
Heliordor: Golden beryl
Goshenite: Colorless beryl.
Morganite: Pink beryl.
Bixbite: Red beryl.
Maxixe: Blue beryl which color fade in sunlight.

Aquamarine is the name given to iron colored beryl which comes in colors from pale blue to rich sky blue or greenish blue.

Aquamarine was named by the Romans over 2000 years ago, derived from words that mean "water of the sea", which is what it reminds one of with its clear blue color.

The preferred color for aquamarine today is rich sky blue. Most aquamarine occurs without any, or very few, inclusions, making it a very eye-pleasing stone.

Because of the shape of the rough that occurs as long prismatic crystals, aquamarine is most often fashioned as a step-cut emerald shape. Fine aquamarine crystals are very appreciated by mineral collectors when they occurs in fine colorful clean hexagonal columns.

Aquamarine is a "dichroic" stone which means that it shows more than one color, depending on which way you look at it. From one view it may appear a rich blue, greenish, or greenish-blue while from another angle it may appear to be nearly colorless.

Nowadays most of the aquamarine in the market owns its deep coloration from heat treatment at 400 to 450 degres of lower colored material. This coloration is stable unlike the possible coloration resulting from irradiation.

Most aquamarine mined today comes from pegmatites in Brazil, but it is also found in alluvial gravels. Fine aquamarines are also found in the Sakangyi area in the west of the Mogok stone tract in Burma (Myanmar). Other occurrences are in Australia, Russia, Madagascar, Afghanistan, Pakistan, Kenya, Mozambique, Namibia, Nigeria, Zambia, and India. Each locality produces a different color variation, sometimes making it possible to identify a stone's origin from color alone.

Aquamarine is brittle and sensitive to pressure. It is also sensitive to high temperature and may loose color if heated to high. Care must be so taken when making some aquamarine jewelry.

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CHYSOBERYL

Chrysoberyl is a beautiful gem by itself. It occurs in yellow, yellowish green or brown color but it is better known for its color change variety:
Alexandrite or by the exceptional "cat's eye" phenomena it can show.

Alexandrite is named for the former czar of Russia, Alexander II, and was first discovered in the Ural Mountains of Russia, supposedly on the day of his birth.
Chromium gives alexandrite its color change property fluctuating between green in fluorescent or daylight to red in incandescent light.

Cat's eye chrysoberyl is known also as cymophane. The effect is caused by microscopic needle-like inclusions that reflect light into a single dynamic sliver of light running along the center of the cabochon and make it like a living cat's eye.

Simply faceted transparent chrysoberyl gemstones are usually found in yellowish green to green, yellow and shades of brown. It is a very fine gemstone associating beauty and durability.

Typically from granite pegmatites and mica schists (in Russia, Sri Lanka, Madagascar, Brazil) the finest qualities for this rare stone as a mineral specimen or a cut gemstone can be found also in Mogok, Burma (Myanmar), in the pegmatite areas in the west of the Mogok valley in Sakangyi or Barnarmyo, and in different secondary alluvial placers in the Mogok Stone Tract near Mogok, Kyatpyin towns and Barnardmyo village.

Mineral collectors appreciate chrysoberyl crystals for their beautiful twins. The most interesting and researched chyrsoberyl twins are the cyclic twins. These crystals appear hexagonal but are the result of a triplet of three "twins," with each "twin" taking up 120 degrees of the cyclic trilling.

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DANBURITE

Mogok in Burma (Myanmar) produces exceptionally fine straw yellow to bright yellow mineral specimens and cut gemstones of danburite which is usually a colorless stone.
Madagascar recently is also a producer of yellow danburite but all our stones are coming from Mogok.
Light pink colored stones are also known from Charcas in Mexico, which is the most important source for this rare stone.

Danburite is usually found in metamorphosed limestones or in granites associated with low temperature hydrothermal activity. It is also found in evaporites.

Danburite is not a well-known gemstone but is growing in popularity. When it is cut properly, Danburite makes exceptionally flashy gemstones but don't dream to find stunning danburite on every street corner: Mogok's production of bright yellow gems is very low and Danburite is likely to stay a beautiful connoisseur gem!

The origin of danburite's yellow color is unknown to us, it is possibly coming from some rare earth elements but we cannot be sure about this.

First discovered in Danbury Connecticut, it was named after that location. Other than Mogok in Burma, the traditional sources of Danburite are Russell (New York, USA), Charcas (San Luis Potosi, Mexico) Kyushu Island (Japan), Uri (Switzerland) and more recently Madagascar island.

Large Danburite crystals and mineral specimens are exceptionally rare. Small stones are more easy to get.

Like topaz it belongs to the orthorhombic system and forms in wedge shaped prisms, similar to colorless topaz, but may be distinguished by their cleavage (poor in Danburite: perfect in topaz).
Danburite's crystal habits include generally prismatic crystals with a diamond-shaped cross-section. The termination shows a steeply slanted dome that produces a wedge look. It is a contrast to quartz's hexagonal prisms and pyramidal terminations. The crystals also can be rather thin to almost circular or up to a foot long and several inches across.

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DIOPSIDE

The etymological origin of "diopside" comes from the ancient greek "di", which means "two", and "opsis", meaning "vision".

With a hardness of 5.5 on Mohs' scale, diopside is a quite brittle gemstone and for this reason is not commonly used in jewelry but in spite of that is, and for a long time, a nice and interesting piece loved by gem and mineral collectors.

Diopside is usually bottle-green, but some colorless, brownish, black, violet-green varieties can be seen. Most of time transparent, the stone can be fibrous and makes it translucent to opaque. These fibrous inclusions can give "cat's eye" effect in green stones and "asterism" with a "4 arms star" in black stones. But star stones are not common.

Because it is a biaxial stone, diopside can present a more or less important pleochroism, generally showing different tones of green. Diopside can be mistaken with peridot and hiddenite.

The crystal shape is usually columnar, but from the Mogok Valley you will find in our pages some "chrome diopside" crystals, which are a light emerald green variety of diopside, showing unusual character like tabular crystal shape.

The diopside is a calcium magnesium silicate: CaMg(SiO3)2. It means that it's a (clino) pyroxene crystallizing in the monoclinic system and presents a perfect prismatic cleavage.

Diopside generally forms in magmatic rocks, but can also be found in metamorphic rocks. Color is due to chrome (livelier green) or iron (green, brown to black).

In addition to Mogok Valley, chrome diopside is also mined in Kimberley diamond mine in South Africa. Other varieties are found in Italy, Austria (Tyrol), Sri Lanka, Brazil (Minas Gerais), Canada and United States (California). The color of stones will vary with locality.

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KYANITE or DISTHENE

The kyanite is a particular and interesting stone for many reasons and first of them are relating to its name. The name kyanite comes from the old Greek word "kyanos" meaning "blue". Kyanite is also called "disthene", from the association of two ancient greek words: "di" meaning "two " and "stenos" meaning "hardness" because one the most important characteristic of this stone is to have a hardness of 5 (on Mohs' scale) parallel to the length of the prism but a hardness of 7 at right angles to this. For this reason, kyanite is perhaps the best example of directional differences in hardness, which reflect the differing strengths of chemical bonding on an atomic scale.

Kyanite is usually blue color(Gem quality kyanite can be confused with sapphire, tanzanite and spinel), exceptionally, it can be light green or colorless and sometimes grey-dark because graphite inclusions. A white variety is known as rhaetizite in also known but has no gem signifiance.

But in spite of this difference of hardness, kyanite is a quite brittle stone, with a perfect cleavage making the cutting hazardous. Its heat-resistance is not really good and beyond 1350 Celsius degrees, it changes to sillimanite (Which is along with andalousite a polymorph of kyanite: Same chemical formula, but in another crystal structure depending of the conditions of pressure and temperature). Because kyanite is a biaxial stone, it shows a strong pleochroism with different tones of blue. Its common habits are columnar crystal, which often present striae and twins.

Kyanite is an alumino-silicate (Al2SiO5), i.e. it is a (neso) silicate crystallizing in the triclinic system. Iron and chromium can replace aluminum, producing the blue, or greenish, color which is most always confined towards the center of the crystal. The specific gravity varies between 3, 56 and 3, 68, depending on inclusions. Kyanite is found in metamorphic rocks. In Burma it is not mined in Mogok but Moe Nyin in the Kachin State. It is also find in India (Patial and Punjab), Switzerland, Brazil, United States (Virginia, North Carolina).

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ENSTATITE

Enstatite is a mineral that is not commonly known in the world of gems. As a gemstone it is more a collector item but it can also be found in jewelry as a cat's eye but faceted enstatite can also easily be worn as pendants or earrings. Enstatite is considered a slightly soft stone as its hardness is 5.5 on the Mohs scale. However of course the harness is not a concern for mineral specimens..

Gem quality green enstatite which color is due to traces of chromium occurs in South Africa and is called "chrome enstatite" while greenish-brown stones are found in the Mogok Stone Tract of upper Burma (Myanmar). Burmese stones show sometimes some fine cat's eye effect with a thin orange to light brown line on the nearly black background of the enstatite cabochon. Some grayish cat's eye material can be found in Sri Lanka as well. Enstatite usually in lower quality specimens can also be found in parts of India, Europe, Africa, and North America sometimes as water worn bronze colored pebbles that can have a very high sub metallic luster. This enstatite is known as bronzite and is sometimes used as an ornamental stone.

Enstatite is a member of the pyroxene family of minerals and is a magnesium-iron silicate (Mg,Fe)SiO3. It is usually found in metamorphic or igeous rocks and has been found also in some meteorites. Enstatite forms in the orthorhombic crystal system although Enstatite but at high temperatures, enstatite's structure changes to a structure with a monoclinic symmetry, it is called clinoenstatite. Clinoenstatite is a polymorph of enstatite, meaning that it has the same chemistry but a different structure. Anyway most stones are found as alluvial pebbles disguising the crystal's habit. Enstatite crystals with a fine clear crystal shape are rare specimens.

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FELDSPAR and MOONSTONES

Moonstone is the name given to the member of feldspar group that displays a sheen effect (adularescence or schiller). The 2 main categories of moonstones are the traditional "true moonstone" composed of orthoclase and albite and the "rainbow moonstone" which is, in fact, labradorite feldspar and less valuable than the orthoclase variety.

Moonstone body color can range from colorless to white, gray, brown, yellow, orange, green, or pink. But its beauty is in its sheen, which can be white to deep blue and create a sweet color that seems to float across the convex surface of the stone when it is cut en cabochon. This effect is especially beautiful when the stone is displayed on a dark background such as an evening dress.

The sheen effect is caused by the intergrowth of two different types of feldspar with different refractive indexes: These intergrowths result from compatible chemistries at high temperatures becoming incompatible at lower temperatures and thus a separating and layering of these two phases when the stone cools down during its genesis. The resulting shiller effect is caused by a ray of light entering a layer and being refracted back and forth by deeper layers before leaving the crystal. This refracted ray has a different character than the incident one and this produces the moonlike glow.
If feldspar is very common on earth, fine moonstone is quite rare and is becoming rarer nowadays.

Feldspar is the group name applied to several crystalline aluminosilicate minerals that are found in abundance in the earth's crust in many localities throughout the world, especially in pegmatites. Mogok is now the typical origin for the finest moonstones as the traditional mines in Sri Lanka are now closed.

Finest classical quality is known to show both a fine blue sheen and a colorless body color but recently an extremely rare and spectacular "Golden moonstone" from Mogok, Burma (Myanmar) has arrived in the market, and the very few stones produced are sold at very high prices.

Moonstone is considered a sacred stone in India, often displayed on a yellow cloth, also considered a sacred color.

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FLUORITE

The name of fluorite, or fluorspar, comes from the fluor element, which is one of its components, associated to calcium. It was first using as a melt in steel industry and also for the making of fluorhydric acid. Fluorite has a hardness of 4 on Mohs? scale (anyway it is a standard reference between calcite, hardness of 3, and apatite, hardness of 5) and so, because of its brittleness, is no used in jewelry. Furthermore, this stone doesn?t resist to the concentrated sulfuric acid, presents a perfect octahedral cleavage, can be easily broken and finally changes color with temperature.
But fluorite has nevertheless some important gemological interest. As a fact of matter, fluorite shows a great variety of color (pink, green, blue, yellow, violet, colorless, etc?) and can even be bi or tri-color (the crystal showing blue, violet and purple curved bands is known as the Blue-John or Derbyshire spar variety and is found in England). It also presents different kinds of inclusions like 2 or 3-phasis, color zoning, fingerprints, tensions, cracks, etc? For these reasons, much confusion is possible with several stones like emerald and amethyst, for example.
The crystal habit is usually a cube, rarely octahedra or dodecahedra, and most often free of host-rocks. Fluorite is one of the favorite for minerals collectors due to its beautiful shapes and colors.

Fluorite is a calcium fluoride (CaF2), i.e. it is a halogen crystallizing in the cubic system. For this reason, optical properties are the same in all direction. It is so a single refractive stone and doesn?t show any pleochroism. Its specific gravity is about 3,18 and it usually shows fluorescence. Fluorite occurs in magmatic rocks, metallic mines, and also in sedimentary rocks. In addition to Thabeikyin which is a few kilometers on the west of the Mogok valley and produces blue-green stones of quality, fluorite is mined in many places world wide as France (Alpes), Mexique, United-States (Illinois, New Hampshire, Missouri), Canada (Ontario), England, Germany (Saxony, Bavaria, Baden), Czechoslovakia (Bohemia), Nigeria, and also in Italy and Norway.

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GARNET

The word GARNET is derived from a latin word meaning grain, as the rounded physical appearance of its crystals looks like red-kernels of a pomegranate. Garnets to a layman have never meant anything more than cheap red colored stones, though it is not true. Garnet is a family of minerals of various kinds, where the different kinds share similar crystal habits and some similarities in chemical composition i.e. (SiO4). They crystallize in the cubic form and hence are S.R.(ADR) stones.Their specific gravity and refractive index can vary very widely due to its type and amount of inter-mixing. The most reliable test is Spectroscopy as all different elements have different absorption lines.
The two sub-groups of garnets are :

Pyralspites : Aluminum is an integral part of the chemical composition in this group, due to a lot of mixing between its individual members the properties are more variable in this group. The three main types are:
1. Pyrope - This dark red colored stone was in vogue back in the 18th & 19th centuries, looks similar to ruby or spinel but does not have a good lusture like them. It is found in various locations such as Burma, China, Madagascar, Sri Lanka, South Africa, Tanzania, U.S.A., and e.t.c.
2. Almandite - Its red color has a tint of violet, looks like pyrope garnet and can imitate lot of red stones, found in many places like Brazil, India, Madagascar, Sri Lanka, U.S.A., and more recently from Czech Republic and Austria.
3. Spessartite - This Orange to red-brown colored stone get its name from the word 'Spessart' meaning forest. Deposits are found in parts of Burma, Brazil, China, Kenya, Madagascar, Sri Lanka, Tanzania, and U.S.A., though the best quality is from Namibia ( Mandarin Spessartite ). In some cases it can be confused for Andalusite, Chrysoberyl, Fire Opal, Hessonite,Sphene or Topaz.

Ugrandites : This group containing Calcium as a basic part of its chemical composition, they keep their own individuality and do not intermix a lot in nature hence showing fairly consistent properties.
1. Grossular - Found in various shades of green, yellow, brown to colorless in nature has four main types. Hessonite is the brown red variety found in Sri Lanka, Brazil, India, Canada... A green colored (emerald look-a-like) garnet called Tsavorite was found in early 1970's in Kenya, and Tanzania. The colorless Leuco Garnets are found mainly in Canada, Mexico, and Tanzania. Hydrogrossular or the falsely called "Transvaal Jade" or "Garnet Jade" is an opaque greenish variety found in South Africa, Burma, and Zambia.
2. Andradite - Demantoid is un-disputably the most valuable garnet found, as the name suggests it has a lusture like a diamond and has the color of an emerald. Its unique horsetail inclusion can also add to its price as its quiet a collector?s item. It is found mainly in China, Korea, Russia, and U.S.A. Melanite is a blackish variety found in Germany, France, and Italy, mainly used for mourning jewelry. Topazolite is a light yellow topaz-like stone found in the Alps of Italy & Switzerland, and parts of California.
3. Uvarovite - This green colored stone very rarely comes in gem quality and can be confused for a dementoid or emerald. Deposits are found in Finland, India, Canada, Poland, and the Urals (Russia).

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PERIDOT

Mogok in Burma is known to produce the best quality for peridot with its two mines near the Barnardmyo villages: Pyaung Gaung and Zalat Thaung.

Pakistan is also renowned for the exceptional quality of its stones but most of the peridots in the market nowadays are coming from San Carlos in Arizona, USA and China.
Chinese and US peridots are plentiful but their color is much more yellowish green than their Burmese or Pakistani counterparts.
Egypt is an important historic source. The Myanmar, Pakistani and Egyptian gems are rarer and of better quality and thus quite valuable, approaching the per carat values of top gemstones.

Peridot is the gem variety of peridotite, which is a very common mineral in the earth's crust. But Peridots are found in ultra basic rocks mostly in hard rock mines.

Lilipad is a typical diagnostic inclusio found in many peridots: It shows a disk-like liquid surrounding a dark octahedral chromite crystal.

The Romans referred to "Peridot" as the "Evening Emerald" because the color did not darken at night and was visible under a lamplight. Some traders still call it the "Night Emerald" but this name should not be used now as peridot is less valuable than emerald.

The most valuable color for peridot is pure green and so any yellow present decreases the global stone value. The qualities of the peridot color also increase with the size of the stone and small size, top-color peridot is nearly impossible to find.

As most Burmese peridot mines in Mogok are government owned, the Burmese government gem auctions in Yangon attract many peridot foreign dealers. A few fine peridots are found in the limitated Burmese private market.

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LAPIS LAZULI

Chemistry: Lazulite (Na, Ca) 8(AlSiO4) 6[(SO4, S, Cl) 2], Sodalite, Calcite, Haüyne, the chemistry changes depending on the deposit and the places inside it.
Specific gravity: 2,5-3,00, more if a lot of pyrite is present
Hardness: 4,5-5 in the Mohs’s scale
Color : ultramarine blue, greenish blue, violetish blue

This stone is not really a mineral like most others gemstones, it is in fact classified as a rock Indeed it is a complex mix of different minerals, mostly Lazulite, which gives its wonderful ultramarine blue, but also Calcite, Sodalite, hauynite and the typical inclusions of pyrite : « the gold shine by spots » say Pline the Old in his Historica Naturalis. That’s mostly what differentiates it from its cousin, the Sodalite which can be very close in appearance.

The Lapis has been used since very ancient times, the first traces of it in the jewelry are over nine thousands years old. Occurring in Babylonian mausoleums, Egyptian pyramids and also in the pre-Columbian civilizations, it’s a symbol of luck and friendship and was also supposed to guide the dead into the hereafter. It’s name is a compound of „lapis“, the Latin word for stone, and the Arabic word „azul“, denoting its colour, as blue as the sky. Curiously, most of these antique stones were found to come from the world’s major deposit: Afghanistan. It was so rare and appreciated that one made thousands and thousands of miles by feet, camels and horses in order to bring it to the final customer, of course at a substantial price. That’s the story of all antique caravans.
But the Lapis was not only used as a jewel; it was also renowned as a pigment in the noble art of painting, especially in the Renaissance. The better blue was obtain by mixing resin, olive oil and mastic with the crushed stone, according to the recipe of the XIIth century’s monks.

Let’s talk about the deposits. The most renowned and virtually all the best quality Lapis comes from Afganisthan, in the little valley of Sar-e-Sang, where no car can penetrate due to the very bad roads, the only mean of transportation is the mule. That’s why no huge blocks can be found on the market, the biggest are those a mule can carry.
The Lapis can only be found in small deposits, mainly primary ones like in Chile ( Flor de Los Andes), Russia ( Baïkal lake, one near the well-named Lazurnïa river), USA ( Colorado and California), Canada and Italy . It occurs also in Myanmar, at Thabanpin near Mogok, where there are two deposits, the first is primary and the second is alluvial (the origin of which remains unknown by non-locals).

Common enhancements for this stone are dyeing and coating, with wax or resin in order to improve the luster, and when the stone has been dyed, it stabilizes the colorant which can be constant or not, depending on its chemistry and the porosity of the material. These treatments can be detected by the hot point method for the coating and in testing the dyeing with acetone on a swab of cotton or checking the stone to look for color concentrations. Some others stones can also be dyed in order to imitate Lapis but none have its specific appearance and these imitations are easily recognizable. Harder to find is the synthetic Lapis, produced by Gilson, it has the same same optical and physical properties, but hopefully not really the same visual aspect. This synthetic has an overall uniformity of grain size and color, and the pyrite inclusions that can occur don’t seem like the natural one. A specialist can easily make the difference with the naked eye.

The best quality of Lapis Lazuli is the ultramarine one, uniform in color, with just a few pyrite inclusions which improve its specific blue by contrast.

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PETALITE

The name petalite comes from the old greek word "petalon" which means "leaf", refering to the leave like disposition of its cleavage which is perfect. Crystal habits are rare and petalite is usually found massive and polysynthetic. It has a hardness of 6 on Mohs' scale, so it is not used in jewelry. In fact, petalite is mostly a collector's piece. In the Molo mining area near Momeik in Burma colorless Petalite was found 2 years ago associated with tourmaline, hambergite, quartz and feldspar in a pegmatite. Crystals there are quite exceptional as they can be found large enough to be cut as gems and fine enough to please crystal collectors. Molo Petalite shows often an etched surface and is locally called "Molo Thalin" or "castorite". Several cut stones up to 20 carats have been seen recently in Burmese markets but supply is scarce as this stone is difficult to cut.
Petalite can be colorless as in Molo or grey, yellow, pinkish or white. A variety showing a chatoyancy is found in Zimbabwe and is called "petalite-analcime". Cat's eye specimen have also been seen in Burma due to tube like inclusions. Some confusion is possible with orthoclase and generally with all kind of transparent man-made glass.
Petalite is a lithium aluminium silicate ( LiAlSi4O10) crystallizing in the monoclinic system. Although petalite is a biaxial stone, it doesn't show any pleochroism. It has a specific gravity varying between 2,4 and 2,6. It usually occurs in granite pegmatites with quartz and lepidolite. Outside Burma, this rare stone can be also found in Sweden, United-States (Massachussetts, Maines), Brazil (Minas Gerais) and, as told above, in Zimbabwe.

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PYRITE, HEMATITE and IRON ORES

Minerals containing iron are called "iron ore". Some confusion is possible between them. They are all opaque, with a strong metallic luster and a specific gravity higher than 4.

Marcassite and Pyrite (also called marcassite's jeweler) are two iron sulfides having the same chemical formula (FeS2) but a different internal structure: pyrite crystallizes in the cubic system and marcassite in the orthorhombic one. They are so called polymorphs. Habits are usually a cube, hexahedron, octahedron, pyritohedron (special kind of 12 five-sided face figure) or tabular crystals, often gathered for marcassite. Striations can be seen on each side and they often present interpenetrated twins. Color is yellowish bronze. They have to be manipulated with a special care because their high rate of suffer can become toxic when heated or in contact with water. They both show an imperfect cleavage, have a SG slightly varying around 4.8 or 4.9 and a hardness of 6-6.5 on Mohs' scale. They occur in magmatic rocks, hydrothermal or sedimentary rocks and are mined in USA (Colorado), Italy (Elba), Greece, Spain, Sweden and South Africa (Transvaal).

Hematite is an iron oxide. Its chemical formula is Fe2O3 and it crystallizes in the trigonal system. Habits can be cubic or rhombohedric but are generally massive, compact or tabular. The color is blue-black or gray-black. It has a hardness of 6.5 on Mohs' scale and its SG range is from 4.95 to 5.28. It can be confused with hematite (but without its magnetic properties, although some hematite specimens found in Brazil seem to have) or psilomelane. It also can be used to imitate black pearls. It occurs in magmatic, sedimentary and metamorphic rocks and is mined in USA (Minnesota), Italy (Elba), Russia (Oural) and Brazil (Minas Gerais).

Chalcopyrite (CuFeS2), which means "pyrite of copper", is a sulfide of copper and iron and is, in fact, an important copper ore. It crystallizes in the tetragonal system and it has a hardness of 3.5-4 on Mohs' scale. Its SG is near to 4.2. Its color is yellowish, deeper than pyrite color. It is mined all around the world.

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RUBY

Burma (Myanmar) is famous for producing the greatest amount of top quality ruby with a fine, clear, deep-red color. Most of the best quality ruby comes from the Mogok Valley in Burma and others from newer sources such as Mong Shu (discovered in the Shan State in 1991), and Namya, in the Kachin State, which experienced a rush in 2000.

"Pigeon blood" was once the paramount color for ruby but this appellation is now tricky as there is no standard behind it. Ruby can be true red or red with some purple or orange overcast or going towards pink. On the last point, the fact is that ruby and pink sapphire are basically the same stone as they are both aluminum oxide with a small amount of chromium. High levels of chromium give red, lower concentrations give pink. There is no clear and worldwide-accepted borderline between what is a ruby vs. a pink sapphire.

Rubies in Mogok and Mong Shu are found either in marble primary deposits in the mountains around the valley or in alluvial placers in the valley. In Namya they are exclusively found in alluvial deposits in this swamp area. All Burmese rubies were born from a metamorphic process (as well as Vietnamese, Nepalese and Afghan stones). They are usually poor in iron, and as a result, show a strong red fluorescence which make them different from their cousins from basaltic deposits in Thailand or Africa. Rubies usually occur in Burma as tabular crystals with hexagonal prisms. Usually the basal plane shows markings consisting of striations, often as equilateral triangles, and prisms are commonly striated horizontally. Mogok also produces some more rare ruby crystals in which rhombohedrons are so well developed that the stone looks similar to a spinel crystal. For many centuries red spinels and rubies were associated with one another and believed to be the same stone.

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SCAPOLITE

Scapolite owns its name from the greek meaning "shaft" as it is usually found as long prismatic rod like crystals.
Gem quality scapolite was originally discovered in 1913 in the Mogok Stone Tract in upper Burma (Myanmar). There, white, pink, yellowish or violet stones of high quality are found. Many of these stones can be cut into cabochons with fine cat's eyes. Since the discovery in Burma, other gem quality stones have been found in Madagascar, Mozambique, Brazil, and Kenya.

Scapolite is commonly not seen as a cut gemstone in fine jewelry with the exception of the exquisite cat's eyes gemstones it can produce. Such fine gemstones are still very rare gemstones as the material is not abundant. It can be quite transparent with fine color. Faceted stones are searched to make a nice addition to any gemologist's compilation. The hardness of the mineral makes it best suited for pendants or earrings. Otherwise, it is an interesting mineral to add to a collection.

Because scapolite is a mixture of minerals, the specific gravity and refractive index will vary. However, most stones have a hardness near 6 on the Mohs scale. Some yellow scapolite may be confused with citrine or yellow beryl. One method to differentiate scapolite from these other stones is by the use of a long-wave ultra-violet light. Scapolite can fluoresce with a yellowish to orange color. Quartz and beryl do not display such fluorescence.

The mineral scapolite, also known as wernerite, is actually a series of minerals run from marialite (Na4Cl(Al3Si9O24)) to meionite (Ca4(SO4CO3)(Al6Si6O24)). This means that the scapolite series of minerals are silicates of aluminum with calcium and sodium. This mineral crystallizes in the tetragonal system and individual crystals may have a short prismatic habit with terminated with low pyramid faces. Scapolite is typically found in metamorphic or less commonly igneous rocks.

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SAPPHIRE

Blue is the most popular color for sapphire but sapphires can be found in nearly every imaginable color:

Sapphire is the gemstone trade name for the gemstones issue from the mineral corundum species with colors different than red. Red corundum is "ruby"
Sapphire used alone means in fact "blue sapphire"

Fancy sapphires is the gem trade name for corundum with an other color than blue or red. They can come in shades of purple, green, yellow, black, all colors except red, as "red sapphire" again is ruby.

Padparadsha sapphires are the most valuable of all fancy sapphires is the their color is close to the color of a lotus flower. In fact, it should be a delicious mix of pink, orange and yellow. Padparadsha are typically coming from Sri Lanka, but natural padparadsha from Mogok in Burma are also known.

Royal blue is the typical color of Burmese sapphire from Mogok it is slightly violetish blue to true blue.

Cornflower blue is more velvety and typically from Kashmir (India), but is also found in Mogok, especially in the Thurein Thaung mine which is famous in Burma as several of its best stones were identified by some major laboratories as being of "Kashmir Origin".

Even after agreeing that origin is not a measure for quality when dealing with gems, the fact is that top quality Burmese sapphires, along with some Kashmir stones, are considered to be the finest quality for sapphire.

In the better qualities, determination of origin for these sapphires is a difficult task. Nowadays production from Mogok is scarce and production in Kashmir is very weak. Most of the sapphires currently in the market are coming from Madagascar and Sri Lanka but Thailand (Kanchanaburi), Cambodia (Pailin), Australia and China are also important producing areas.

Like ruby, many sapphires in the market nowadays owe their beautiful color to heat treatment, and some yellow stones get their color from irradiation.

Chanthaburi in Thailand is the world center for the heat treatment of gemstones which is something of a semi-scientific alchemy. This treatment ensures a steady supply of fine stones at affordale prices for gem-lovers the world over. In fact it has become such an industry standard that "unheated" rubies and sapphires are considered collectors items. They are still the gemstones of the very wealthy as they can attain really very high prices.

Sapphire can present many interesting particlularities that make it one of the crystal and mineral collector favorite:
Its shapes cigar like or bipyramid are very attractive as sapphire comes in many colors. More rare but very appreciated are the hexagonal columnar crystals.

Sapphire in matrix can make very fine stones for displays, but such stones are rare and difficult to find in the market as most of sapphire are coming from alluvial deposits. These deposits can be from former metamorphic or basaltic weathered rocks. Most sapphires in Mogok were formed in feldspar (metamorphic origin) in the west of the Mogok valley near the Kabaing granitic dome. Some sapphires are also found sometimes in the north east of Mogok in strange iron rich matrix or also even more strange completly covered by spinel. Going further north near the Momeik city igneus sapphire are also found showing the incredible geologic complexity of the Mogok area.

Star sapphires are one of the gemstone collector favorite. Star in sapphire can result of 2 kind of inclusions: Rutile needles reflecting light as mirrors and that cross each other with 60 degres angles are the reason of the moving 6 ray star effect.
Hematite platelets give the 6 rays stars in black star sapphires but their orientation is not the same as the rutile needle orientation. This particularity makes 12 rays star stones possible if both rutile and hematite are present inside the stone.

Trapiche sapphire are an other kind of "star sapphire" in this case the star is not moving at all at it is not the result of the reflection of light on mirror like needles but in this case this is more a special color zoning inside the crystal. Such stones are very rare but are known in Burma. Trapiche star sapphire are possible: They show the 6 ray non moving trapiche star and a 6 rays moving star from rutile needles!

Sapphire is really an interesting gemstone.

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SPINEL

The origin of the name "spinel" is uncertain. Spinel can be found in many colors such as red, pink, blue, green, orange; fine red and blue spinels are considered among the most valuable gemstones.

Spinel is a relatively unknown stone to the general public, and this is a pity as this is one of the most beautiful gemstones available. The point is that spinel's rarity hasn't motivated any major company to promote it because if the demand were to rise, the supply would not be plentiful enough to keep up with it. Therefore, spinel remains mostly a stone for the connoisseur, for those who love it for its combination of excellent durability, fine pure red color and high brilliancy.

Spinel is the near perfect wedding of ruby and diamond qualities! Spinel is so close to ruby that for years it was mistaken as ruby and its common misnomer was "Balas Ruby".
Actually, the 2 most famous rubies:

The "Black Prince Ruby",
The "Timur Ruby",

both from the British Crown Jewels, are actually red spinels.

The finest quality red spinel comes from Mogok in Burma (Myanmar) with a deep red color that matches the color of most rubies.
Another source of Burmese top quality spinel has been discovered in Nanyazeik (or "Namya" in the Kachin people's language). These rare but exceptional spinels can reach a hot pink color as saturated and fluorescent as candy.

Spinels are also found in Vietnam, Sri Lanka, Tanzania or Russia but without reaching the Burmese color qualities.

Spinel (MgAl2O4) belongs to the cubic system. It is found as a metamorphic mineral as marble, and also as a primary mineral in basic rocks, because in such magmas, the absence of alkalis prevents the formation of feldspars and any aluminum oxide present will form corundum or combine with magnesia to form spinel. This explains why spinel and ruby are often found together.

In terms of quality, top stones combine eye-clean clarity with an intense color, without any secondary brown tones. But such stones are very rare. One reason is that, unlike ruby, there are no known treatments to improve spinel color. Of course a spinel with a filled fracture can be found once a while but usually stones in the market are usually just polished and cut!

You can just dream to get the small quantity of fine gems that the mines produce.

Regarding current prices in the market, spinel is very under valued compared to ruby, an equivalent fine quality is around 10% of the price of ruby, but top spinels may be 100 times more rare! Fine red spinels are real investment stones.

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TOPAZ

The Mogok stone track with its western pegmatic areas in Sakangyi and Barnardmyo is a famous place to find topaz mineral specimens and crystals that are then cut as fine gemstones.
Natural blue, sherry, pink and large colorless specimens are found there.

Most natural colored topaz especially brown and blue are naturally fading under sunlight. Some brown topaz hosting some chromium atoms can then turn pink after direct exposure to sunlight.

Topaz comes mainly from Minas Gerais in Brazil, Russia, and Madagascar. Topaz occurs naturally in colorless, yellow, orange, red, blue and green body colors. Colorless topaz has little value and is common in the market. Some topaz varieties can be irradiated to make its color become various shades of blue. Today, irradiated blue topaz is so common in the market that this practice is accepted by most countries except, for example, in France where just the rare, natural blue topaz can legally be sold. Red-brown topaz is also common. It can make a nice faceted stone and is sometimes called "sherry" topaz. Again it is not of high value.

Topaz is typically more expensive than citrine, and far less than morganite, or good golden beryl.

"Imperial" Topaz is the most prized color in topaz it is coming typically from Brazil with a red-orange to a pink-orange color. It is heat sensitive, and usually contains numerous flaws. In fine qualities these stones can reach about the same value as good aquamarines.

Pink and green topaz is fairly rare and highly valued. Pink color is occasionally found in jewelry, but the green is very rarely found.

Topaz has an orthorhombic crystal system with some pseudo tetragonal symmetry and is easily differentiated from other transparent minerals, like quartz, by its vertical striations, its high specific gravity and luster. Topaz represents a link between pegmatic and hydrothermal growing phases. As a result it can harbor many interesting pegmatic crystals such as albite, apatite, goethite, muscovite and its congruence with hydrothermal growing environment explain the richness of its liquid inclusions.

Inclusions in topaz can be beautiful and topaz spheres hosting inclusions are as a result very appreciated as paperweights or decorative items.

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TOURMALINE

Tourmaline occurs in a wide range of colors. It is one of the most favored gemstones for mineral specimens and cut gems collectors due to its incredible variety of colors and the beauty of its crystals.

Most tourmalines are known in the gem trade by the variety name following their color:

- Rubellite :Pink to red but also brownish, purplish or orangy, its color is usually due to manganese and iron.
- Verdelite :Yellowish green to bluish green, it is usually colored by iron.
- Indicolite: violetish to greenish blue.
- Paraiba: electric blue typical from Paraiba area in Brazil.
- Chrome tourmaline: Intense green color, own its color to chromium.
- Achoite: Colorless.

For the mineral collectors, tourmaline group varieties are better known by more scientific names dealing more with the composition and the structure of the stone:

- Dravite: typically yellow to brown can be red also.
- Schorl: Sodium and iron rich, Black.
- Elbaite: Sodium, aluminium, lithium rich, Many colors possible.
- Ferridravite: Magnesium and iron rich, Black.
- Chromdravite: Sodium, magnesium and chromium rich, Dark green.
- Buergerite: Sodium and iron rich, Bronzy brown.
- Liddicoatite: Calcium, Lithium, aluminium rich, many colors possible.

Highly saturated tourmalines with fine clarity will be highly priced with some exceptions, such as for Rubellite which even highly inlcuded can get high value.

Burma (Myanmar) is known for its fine tourmalines, which are mined in Mogok (most varieties), the Molo pegmatic area near Momeik is a lithium and beryllium rich pegmatite area that host very fine Schorl and exceptional fibrous "mushroom" like elbaites) and the Shan and Kayin states (green tourmaline). But most of the tourmaline commonly in the market is now coming from Brazil and Madagascar.

Tourmaline forms as a trigonal crystal in a variety of geological settings; as an associated mineral in metamorphic rocks as gneiss or schists, as long prisms in granitic pegmatites usually with a feldspar matrix, or as single crystals after alteration of the pegmatite resulting, for example, in kaolinisation. In these granite pegmatites it occurs in the immediate vicinity in the enclosing host rocks.

Pegmatitic tourmaline is commonly black and is associated with quartz and feldspar. The light colored gem tourmalines are much more rare, usually occurring in pegmatite core zones. Other occurrences for tourmaline are in hydrothermal veins where heated mineral bearing liquids or gases from deep igneous sources later cooled and crystallized along rock fractures, in granites due to late stage alteration of micas and feldspars by boron containing fluids, and by boron metasomatism in contact and regionally metamorphosed rocks. Some tourmaline bearing mica schists may have formed by regional metamorphism of argillaceous sediments containing evaporate borates. Because of tourmaline's relatively high hardness and specific gravity, it is often found in elluvial and alluvial deposits as for example in the gravels of Mogok in Burma or in those of Sri Lanka.

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QUARTZ FAMILY: AMETHYST, CITRINE, AGATE...

The name quartz comes from the German miners' language used during the Middle Age, but its meaning is still not understood.
Quartz is a silicon dioxide and its chemical formula is SiO2. It crystallizes in the trigonal system and has no less than 8 polymorphs (i.e. crystals having the same chemistry but a different internal structure), but, contrary to quartz, are extremely rare and need high temperature and/or pressure condition to be stable. Quartz belongs to the silica group which is a subdivision of the (tecto) silicate class.
Habits are usually a 6-faces prism ended by pyramid but can also be tabular, or show a druse or massive form. Horizontal striae are an important characteristic and are due to the vibration during the crystal growth. It often presents twinning. Crystals are generally important and some pieces bigger than a human-being can be found (Brazil). Quartz has a hardness of 7 on Mohs' scale, where it is a standard-reference and so an important boundary in gemology. In a matter of fact, many of the dust particles in the air are also quartz. So a gem has to be hard enough (i.e. having a hardness equal or higher than 7 to resist abrasion if is daily worn).
Quartz has some attractive properties, which are used by industries as optical lenses, electrical components, for example.
Quartz is, after the feldspar, the most common mineral on the crust part of Earth (13%) and is the principal component of magmatic, metamorphic acid rocks and sandstone.
Quartz is an important family and shows an amazing variety of colors and forms. It is subdivided into 2 categories: macrocrystalline and cryptocrystalline quartz.

Macrocrystalline means "large crystals". Many varieties are well known, popular and show a nice clarity and color.
Amethyst is the violet common-quartz variety used in jewelry owns its color to color centers.
Citrine is the yellow to orange quartz variety. Most of the stones in the market are in fact resulting from the heat treatment of amethysts.
Smoky quartz is the brown variety, rock crystal the colorless.
Quartz is also very rich in inclusions and more than 200 different minerals were identified only in European Alps specimens. Rutilated quartz is may be the most famous and researched: It holds beautiful yellow rutile needles. Aventurine shows aventurescence tue to small reddish platelets of hematites randomly distributed within the stone.
Quartz are also the variety showing phenomena like the chatoyancy in the "tiger's eye" for example. This particular stone is interesting as quartz in fact had replaced a former mineral: crocidolite and as a result has taken its fibrous structure given the special chatoyancy. This phenomena is called pseudomorphism.

Cryptocrystalline (from the Greek word "crypto" meaning "hidden") refers to the crystals which are too small to be seen even through a microscope. They usually react as an aggregate through a polariscope. Crystals from this variety are semitransparent to opaque. Although taken in the large meaning chalcedony is a cryptocrystalline synonymous, stricto sensu chalcedony is the biggest subdivision of this category with many stones as chrysoprase (light green), sard (brownish red) and even fossilized wood (i.e. has been entirely replaced by chalcedony preserving the original shape; it is pseudomorph as "tiger eye"). Another subdivision gathers all kinds of agate (e.g. moss agate, dendritic agate, etc?) while the last one concerns the jasper (e.g. heliotrope).

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ZIRCON

Not to be confused with the synthetic "cubic zirconia" (or "CZ") which is a laboratory creation and is never found in nature, zircon is a completely natural beautiful and fine gemstone.
Zircon has been known since ancient times. It is said that its name came from the Arabic and Persian word zargoon which means golden colored. This gemstone can appear in colors other than golden yellow. These colors include: red, brown, green, blue, and colorless.

Zircon has many special properties that make it quite unique and interesting:

First of all, zircon has a very high refractive index. This means that it has the ability to strongly bend light. In fact, the high refractive index of zircon is similar to that of diamond. This stone also has a high dispersion or "fire". Long ago, colorless zircons were known as "Matara Diamonds" as these stones were mined in Matara, Sri Lanka.
A second distinctive property of zircon is that it is found in a "low" and "high" type. These two types of zircon are separated by their difference in refractive index and specific gravity. As you might guess, the "high type" has a higher refractive index and specific gravity than the "low type". "High type" zircons show a very strong birefringence. This particularity, shared with peridot, makes the stones appear fuzzy. On the other hand "low type" zircon can be near amorphous and sometimes show a very low biregringeance.
The difference between the two types results from the decay of uranium and thorium that are naturally present in zircon. The crystal structure of the "low type" zircon has been damaged over million of years by this radioactive decay. Therefore, this degraded zircon is known as metamict. Anyway their low uranium content is absolutely not dangerous for human health as low levels of radioactivity are common in nature in zircons as well as in most granites for example.
Greenish brown Burmese zircons from Mogok, Burma are very famous in gemology schools as they displays a special absorption spectrum with many absorption lines commonly known as "jailhouse". But other types of zircons and especially the red one usually show no spectrum at all.

Pure zircon has the chemical composition zirconium silicon oxide (ZrSiO4) and forms in the tetragonal crystal system and often appears in square prisms with square pyramid terminations. Zircon occurs in many locations around the world including Australia, France, Nigeria, Burma (Mogok), Vietnam, Cambodia (Pailin), Thailand (Chanthabury), and the USA. Gem quality material typically comes from Vietnam, Cambodia, Thailand, and the Mogok Stone Tract of upper Burma. Many of these stones are heat treated to create the beautiful transparent yellow and blue gems common in jewelry. Natural blue zircon is extremely rare.

Zircon is a natural and desirable stone as a gem or as a crystal specimen. The prices of this mineral are quite affordable considering it is such a fascinating material. A mineral collection is not complete without at least one fine specimen of zircon

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American Gemstone Authority LLC