The American Gem Society (AGS) is a trade association of professional gemologists founded in 1934 by Robert M. Shipley, who also founded the Gemological Institute of America (GIA). Members are held to a high code of ethics with emphasis on consumer protection. American Gem Society"

Amethyst (SiO2) is a violet or purple variety of quartz often used as an ornament. The name is generally said to be derived from the Greek a, "not," and methuskein, "to intoxicate," expressing the old belief that the stone protected its owner from drunkenness. It was held that wine drunk out of a cup of amethyst would not intoxicate. However, the word may probably be a corruption of an Oriental name for the stone. Amethyst"

Ametrine, also known as Trystine, is a naturally occurring variety of quartz. It is a mixture of amethyst and citrine with zones of purple and yellow or orange. Almost all commercially available ametrine is mined in Bolivia, although there are deposits being exploited in Brazil and India. Ametrine"

Ammolite is a rare and valuable opal-like organic gemstone found primarily along the eastern slopes of the Rocky Mountains of the United States and Canada. It is made of the fossilized shells of ammonites, which in turn are composed primarily of aragonite, the same mineral that makes up nacreous pearls. It is one of the three biogenic gemstones, the other two being amber and pearl. 1 In 1981, ammolite was given official gemstone status by the World Jewellery Confederation, the same year commercial mining of ammolite began. In it was designated the official gemstone of the Province of Alberta. Ammolite"

Anyolite is considered a variety of the mineral zoisite. Found in Kenya and Tanzania, anyolite is actually a metamorphic rock composed of intergrown green zoisite, black hornblende, and ruby. It is said to be named after the Maasai word anyoli, meaning "green." Anyolite is also referred to as ruby in zoisite or Tanganyika artstone. Anyolite"

Aquamarine (Lat. aqua marina, "water of the sea") is a gemstone-quality transparent variety of beryl, having a delicate blue or bluish-green colour, suggestive of the tint of sea-water. It's closely related to the emerald. Aquamarine"

In gemmology, an asterism is an optical phenomenon displayed by some rubies, sapphires, and other gems of an enhanced reflective area in the shape of a "star" on the surface of a cabochon cut from the stone. Asterism (gemmology)"

Aventurine is a form of quartz, characterised by its translucency and the presence of platy mineral occlusions that give a shimmering or glistening effect termed aventurescence. The most common colour of aventurine is green, but it may also be orange, brown, yellow, blue or gray. Aventurine"

Benitoite, whose name derives from its type locality ( San Benito County, California) is a blue silicate mineral, found in hydrothermally altered serpentinite. Benitoite fluoresces under ultraviolet light, appearing light blue in color. Benitoite"

The mineral beryl is a beryllium aluminium cyclosilicate with the chemical formula Be3Al2(SiO3)6. The hexagonal crystals of beryl may be very small or range to several meters in size. Terminated crystals are relatively rare. Beryl exhibits conchoidal fracture, has a hardness of 7.5-8, a specific gravity of 2.63-2.80. It has a vitreous lustre and can be transparent or translucent. Its cleavage is poor basal and its habit is dihexagonal bipyramidal. Pure beryl is colorless, but it is frequently tinted by impurities; possible colors are green, blue, yellow, red, and white. The name comes from the Greek beryllos for the precious blue-green color of sea water. Beryl"

Bisbee Blue refers to the turquoise that comes from copper mines located in the vicinity of Bisbee, Arizona. It is also called Bisbee turquoise. Bisbee Blue"

Bixbite (also known as red beryl, red emerald, or scarlet emerald) is a red variety of beryl, Be3(Al,Mn)2Si6O18. It is very rare, only known to occur in a few locations in the western United States and one in Mexico. Bixbite was named after Maynard Bixby. Bixbite"

A cabochon or cabouchon is a gemstone which has been shaped and polished as opposed to facetted. The resulting form is usually a convex top with a flat back, although the term is used to mean any deliberate shape that is not facetted. Cutting "en cabochon" is usually applied to opaque gems, while facetting is usually applied to transparent stones. Hardness is also taken into account as softer gemstones with a hardness lower than 7 on the Mohs hardness scale are easily scratched, mainly by silicon dioxide in dust and grit. This would quickly make translucent gems unattractive, whereas polished as cabochons, the scratches would not be as easily apparent. Cabochon"

Cairngorm is a variety of quartz crystal originally found in the Cairngorm Mountains of Scotland. It usually has a smokey yellow-brown colour, though some specimens are a grey-brown. Like other quartz gems, it is a silicon dioxide crystal, with a small amount of ferric oxide impurity which gives it the characteristic colour. Cairngorm"

Carnelian beads (other variants of the name include Cornelian beads, sadoine, Mecca stone, and pigeon’s blood agate) is a gemstone jewelry made of carnelian quartz. The mineral is found worldwide, but India is most reputed for developing the best gemstones. Carnelian beads"

Chlorastrolite is a green or bluish green stone, usually with finely radiated or stellate masses. Stellate masses tend to be chatoyant. It can be subtranslucent to opaque. It is a variety of pumpellyite: Ca2(Mg,Fe)Al2(SiO4)(Si2O7)(OH)2·H2O. Chlorastrolite was once thought to be an impure variety of prehnite or thomsonite. Chlorastrolite"

The mineral or gemstone chrysoberyl, not to be confused with beryl, is an aluminate of beryllium with the formula BeAl2O4. Chrysoberyl is transparent to translucent and sometimes opalescent. An interesting feature of uncut crystals of chyrsoberyl are the cyclic twins called trillings. These twinned crystals have a hexagonal appearance, but are the result of a triplet of twins with each "twin" taking up 120 degrees of the cyclic trilling. The word chrysoberyl is derived from the Greek words meaning golden and beryl. Chrysoberyl"

Chrysoprase (also chrysophrase) is a gemstone variety of chalcedony (fibrous form of quartz) that contains small quantities of nickel. Its color is normally apple-green, but varies to deep green. It is cryptocrystalline, which means that it is composed of crystals so fine that they cannot be seen as distinct particles under normal magnification. This sets it apart from rock crystal, amethyst, citrine, and the other varieties of crystalline quartz which are basically transparent and formed from easily recognized six-sided crystals. Other members of the cryptocrystalline quartz family include agate, carnelian, and onyx. Unlike many non-transparent members of the quartz family, it is the color of chrysoprase, rather than any pattern of markings, that makes it desirable. Chrysoprase"

Citrine, also called citrine quartz or citrine topaz, is an amber-coloured gemstone. It is a form of quartz with ferric iron impurities, and is rarely found naturally. Most commercial citrine is in fact artificially heated amethyst or smoky quartz. Brazil is the leading producer of naturally mined citrine, with much of its production coming from the state of Rio Grande do Sul. Citrine"

Clinohumite is an uncommon member of the humite group of minerals, a magnesium silicate according to the chemical formula (Mg,Fe)7(SiO4)3(F,OH)2. Most commonly found as tiny indistinct grains, large euhedral clinohumite crystals are sought by collectors and occasionally fashioned into bright, yellow-orange gemstones. Only two sources of gem-quality material are known: the Pamir Mountains of Tajikistan, and the Taymyr region of northern Siberia. It is one of two humite group minerals that have been cut into gems, the other being the much more common chondrodite. Clinohumite"

Cubic Zirconia (or CZ) is zirconium oxide ( ZrO2), a mineral that is extremely rare in nature but is widely synthesized for use as a diamond simulant. The synthesized material is hard, optically flawless and usually colorless, but may be made in a variety of different colors. It should not be confused with zircon, which is a zirconium silicate (ZrSiO4). Cubic zirconia"

Datolite is a calcium boron hydroxide nesosilicate, CaBSiO4(OH). Datolite crystallizes in the monoclinic system forming prismatic crystals and nodular masses. The luster is vitreous and may be brown, yellow, light green or colorless. The Mohs hardness is 5.5 and the specific gravity is 2.8 - 3.0. The type localities are in the diabases of the Connecticut River valley and Arendal, Aust-Agder, Norway. Associated minerals include prehnite, danburite, babingtonite, epidote, native copper, calcite, quartz and zeolites. It is common in the copper deposits of the Lake Superior region of Michigan. It occurs as a secondary mineral in mafic igneous rocks often filling vesicles along with zeolites in basalt. Datolite"

Demantoid is the green gemstone variety of the mineral andradite, a member of the garnet family of minerals. Andradite is a calcium- and iron-rich garnet, and is a distinct mineral species from the aluminum- and iron-rich reddish almandite garnets typically seen in jewelry stores. It is the most expensive and rare of garnet gemstones, with fine specimens commanding prices of thousands of dollars per carat. Demantoid"

This article addresses the many imitations of diamond. For a broader discussion of diamonds, see diamond. For other uses of the word diamond, see diamond (disambiguation). Diamond simulant"

Dioptase is an intense emerald-green to bluish-green copper cyclosilicate mineral. It is transparent to translucent. Its luster is vitreous to sub- adamantine. Its formula is CuSiO3·H2O (also reported as: CuSiO2(OH)2). It has a hardness of 5, the same as tooth enamel. It specific gravity is 3.28 - 3.35, and it has two perfect and one very good cleavage directions. Additionally, dioptase is very fragile and specimens must be handled with great care. It is a trigonal mineral, forming 6-sided crystals that are terminated by rhombohedron’s. Dioptase"