Alexandrite Alexandrite is a mineral (a type of chrysoberyl) that appears to be different colours depending on whether it is viewed in natural or artificial light. Alexandrite appears to be red when seen in candle light and blue to green when seen in fluorescent light. Alexandrite was discovered on the birthday of the Russian Czar Alexander II, and it was named in his honour. Alexandrite is mined in Russia, Brazil, Burma, Ceylon, and Rhodesia. Laboratory-produced Alexandrite is common, and it is often sold as natural Alexandrite. Alexandrite has a hardness of 8.5 and a specific gravity of 3.64-3.74.
Citrine Citrine (from the French for "lemon") is a rare, yellow type of quartz, a semi-precious stone that ranges in color from pale yellow to orange to golden brown. The best quality Citrine is found in Brazil. Many of the stones sold asCitrine are actually heat-treated amethysts. Citrine has a hardness of 7 and a specific gravity of 2.65. Chrysolite Chrysolite is a name used for many stones. During Victorian and Edwardian time, it referred to green-yellow Chrysoberyl. It can also refer to Peridot (shown above). Long ago, the name was used to refer to almost any yellowish gem.
Chrysoberyl Chrysoberyl is a hard stone that ranges in colour from yellow, to brown, to green. Some Chrysoberyls include Alexandrite and Cat's Eye.
Amethyst Amethyst (Greek for "not drunken") is a form of the mineral quartz, and is a relatively common gemstone. Amethyst is usually purple, but can range in color from pale lavender to a very deep, reddish purple to a milky color to green. Deeper-coloured Amethysts are more highly valued. The ancient Greeks believed that Amethyst made one immune to the effects of alcohol. Synthetic Amethysts are hard to distinguish from the real stone.
Ametrine
Ametrine is a variety of quartz, a mixture of Amethyst and Citrine. Ametrine is partially purple and partially orange-yellow.
Ammolite Ammolite (also known as Korite, Calcentine, or Buffalo Stone.) is a fossilized, opalized ammonite shell used as a gemstone (it is the shell of the ammonite, a fossilized marine animal, a Cephalopod). It is a grey, iridescent stone with flashes of green, red, yellow, blue or purple (blues and purples are rare); the color changes as the stone is turned. Ammolite has a hardness of about 4 (it is very brittle before it is treated) and a specific gravity of 2.8. Ammolite is usually treated with a colorless, hard material to increase the strength of the stone and is often mounted as a doublet or a triplet (with a quartz top layer and a shale underside). Ammolite is only found in southern Alberta, Canada.
Aquamarine Aquamarine is a transparent, light blue or sea-green stone that is porous. Today, blue aquamarines are more highly valued, but this was not true in the past, when sea-green stones were prized. Heat-treatment turns greenish stones bluer. The best aquamarines come from Brazil. Large aquamarines are relatively common. Aquamarines are usually faceted but when they are cabochon cut, a cat's eye effect or asterism may appear. Aquamarines belong to the beryl family of stones. Aquamarine has a hardness of 7.5-8 and a specific gravity of 2.65-2.85.
Beryl Beryls are a family of gemstone that include emerald, aquamarine, beryl (green), red, morganite (yellow), and heliodor (pink). Beryl has a hardness of 7 - 8, a specific gravity of 2.6 - 2.9, and the chemical formula Be3Al2SiO6. Internal flaws in beryl gems can be hidden by treating the stone with oil (this is often not disclosed to the buyer).
Black opal Black opals are a valuable type of precious opals with a dark ground colour. They are luminous, iridescent, and frequently have inclusions of many colours ("fire"). Opal is a mineral composed of silica (and some water) and is a species of quartz. The rainbow like iridescence is caused by tiny crystals of cristobalite. Many opals have a high water content - they can dry out and crack if they are not cared for well (opals should be stored in damp cotton wool). Opals have a hardness of 5.5 to 6.5 and a specific gravity of 1.98-2.50. Black opals are found in Australia.
Blue diamond Blue diamonds are rare, fancy diamonds and are quite valuable. Diamonds are precious, lustrous gemstones made of highly compressed carbon; they are one of the hardest materials known. Diamonds have a hardness of 10, a specific gravity of 3.5, and a refractive index of 2.417 - 2.419.
Cognac diamond A cognac diamond is a cognac-brown diamond (having a colour of C7). Most cognac diamonds are mined in Western Australia (in the Argyle Mine). The colour is produced by a their low nitrogen content.
Chrome diopside Chrome diopside is an emerald-green coloured gemstone.
It is a chromium-rich variety of the common mineral diopside (Calcium magnesium silicate). Chrome diopside has a hardness of 5 to 6 and a specific gravity of 3.3 to 3.6.
Diamond Diamonds are precious, lustrous gemstones made of highly compressed carbon. Diamonds are one of the hardest materials known. Diamonds have a hardness of 10, a specific gravity of 3.5, and a refractive index of 2.417 - 2.419. Colours of Diamonds range from colourless, yellow, orange, brown, to almost black. Much rare colours are red, blue, green, and purple; these colours (called fancies) are quite valuable. Canary diamonds have a deep yellow colour. A Diamond's value is based on the "4 C's": colour, cut, clarity, and carat weight. A Diamond's colour (saturation) is rated on an alphabetical scale ranging from D (white) to Y (yellow). "Z" Diamonds are fancy, or deep-coloured diamond. A Diamond's cut is designed to maximize the stone's natural "fire"; brilliant cuts are preferred. A Diamond's clarity depends on the number and size of its flaws and inclusions (of other minerals, like quartz). Clarity is rated from FI (flawless), IF (flawless at 10x magnification), a series of V ratings (very small flaws at 10x magnification), a series of S ratings (small flaws at 10x magnification), to I1, I2, and I3 (having inclusions visible to the naked eye). A Diamond's carat weight is simple how much it weighs (a carat is about 0.2 grams or about 0.007 ounces). The largest-known gem-quality Diamonds include the Cullinan (aka the Star of Africa, 530.20 carats), the Excelsior, the Great Mogul (an ancient Indian Diamond which is said to have originally weighed 787.5 carats, but its location is not known and nothing about it has been authenticated), the Darya-I-Nur, and the Hope Diamond (named for a purchaser, Henry Thomas Hope).
Emerald Emeralds are a very hard, green precious stone (beryl, Be3Al2Si6O18, coloured by chromium and some vanadium impurities). Flaws and cloudiness (called jardin) are very common in emeralds, so many emeralds are oiled, irradiated, and dyed to improve their look. Synthetic emeralds (developed by Carroll Chatham in the 1930's) have fewer imperfections and are very hard to distinguish from natural emeralds. Emeralds belong the beryl group of stones of which also includes aquamarine, morganite, and chrysoberyl). Emeralds have a hardness of 7-8 and a specific gravity of 2.6 - 2.8. Emerald (and all forms of beryl) have large, perfect, six-sided crystals. Emeralds were long thought to have healing powers, especially for eyesight. During the renaissance, emeralds were used as a test for friendship among the aristocracy; an emerald given to a friend would remain perfect as long as the friendship endured.
Excelsior diamond The Excelsior is the second- or third largest diamond (depending on whether or not the Braganza diamond was actually a diamond). This irregular-shaped blue-white diamond was roughly 995 carats. It was found in l893 by a worker at the De Beers mine at Jagersfontein, Orange Free State, South Africa. The Excelsior diamond was cut in 1904 by I.J. Asscher and Company of Amsterdam into 21 stones, including a 69.80-carat marquise, an 18-carat marquise stone (which was displayed at the l939 World's Fair by the De Beers company), and many other stones.
Facet A facet is one of the flat surfaces of a cut stone or glass
Fancy diamond Fancy diamonds are rare diamonds that are red, blue, green, or purple; these diamonds are quite valuable. Diamonds are precious, lustrous gemstones made of highly compressed carbon; they are one of the hardest materials known. Diamonds have a hardness of 10, a specific gravity of 3.5, and a refractive index of 2.417 - 2.419.
Fire opal Fire opals are a type of opal that is fiery orange to red in colour (but have no opalescence). These opals are rarely transparent - they are usually milky. Opal is a mineral composed of silica (and some water) and is a species of quartz. Many opals have a high water content - they can dry out and crack if they are not cared for well (opals should be stored in damp cotton wool). Opals have a hardness of 5.5 to 6.5 and a specific gravity of 1.98-2.50. Fire opals are found in Western Australia, Mexico, Brazil, Guatemala, and Honduras.
Garnet Garnets are any of a group of semi-precious silicate stones that range in colour from red to green (garnets occur in all colours but blue). Some garnets used as gemstones include pyrope (the deep red garnet), almandine, spessartine, grossular, the iron-aluminium dark red garnet (also known as the carbuncle stone), Uvarovite (rare), and the lustrous Andradite (which includes the valuable green demantoid garnet, Topazolite , and Melanite). Red garnet is the birthstone for January. Garnet has a hardness of 6-8 and a specific gravity of 3.5 - 4.3. The formula for garnet is: (Mg, Fe, Ca or Mn) with Al2Si3O12.
Green diamond Green diamonds are rare, fancy diamonds and are quite valuable. Diamonds are precious, lustrous gemstones made of highly compressed carbon; they are one of the hardest materials known. Diamonds have a hardness of 10, a specific gravity of 3.5, and a refractive index of 2.417 - 2.419.
Goshenite Goshenite is the pure, colourless form of beryl (Be3AlSiO6, related to emerald and aquamarine). This hard, transparent gemstone is named for the town of Goshen, Massachusetts, where it was first found. Goshenite has been found in North and South America (especially Colombia), Northern Europe, East Africa, South Africa, and the Himalayan mountains in Asia. Goshenite has a hardness of 7.5 - 8.0 and a specific gravity of 2.6 - 2.8. It is not enhanced Goshenite is sometimes coated with a green foil to resemble an emerald.
Hardness A substance's hardness is how resistant it is to being scratched. Hardness is measured using the Mohs Scale of Hardness. In the Mohs scale, one substance is harder than another if it can scratch it. For example, a diamond will scratch garnet, but not the other way around, so a diamond in harder than garnet.
Substance
Hardness
Talc
1
Amber, Fingernail, Ivory, Shell, Jet
2.5
Gold
2-3
Bronze, Coral, Pearl
3
Iron
4
Glass
5
Opal
5.5-6.5
Amethyst, Chalcedony, Quartz,Steel(pocket knife)
7
Spinel, Topaz
8
Ruby, Sapphire
9
Diamond
10
Iolite Iolite (meaning 'violet stone'), also known as water sapphire and lynx sapphire, is a transparent, violet-blue, light blue, or yellow-grey mineral. Iolite is pleochroic; a single stone will show many colours (in the case of Iolite, violet-blue, light blue, and yellow-grey). Iolite is not rare and has a hardness of 7 - 7.5. Iolite is found in Sri Lanka, India, Madagascar and Burma.
Imperial topaz Imperial topaz is golden orange-yellow topaz; it is the most valuable type of topaz.
Kunzite Kunzite is a transparent pink, light pink, or light purple gemstone that resembles rose quartz. It is a variety of the mineral spodumene. Kunzite can fade after prolonged exposure to light. Kunzite is also called "evening stone," because of its propensity to fade in bright light. The original colour of some kunzite stones can be restored or even intensified by irradiation. It is usually used as a large stone and is easily chipped; small stones of kunzite are difficult to cut. Kunzite is often used in pendants. Kunzite has a hardness of 6-7 and a specific gravity of 3.1 - 3.2. Kunzite was first found in 1902 in Pala, California, USA, and is named for the gemologist George F. Kunz. Kunzite's chemical composition is LiAlSi2O6
kyanite Kyanite is a deep sapphire blue, green, grey, or white gemstone. The colour is not always uniform; it can be blotchy or in streaks. The crystals are crystals are transparent to translucent. Kyanite has a hardness of 4.5 to 6.5; the hardness varies depending on which way it is scratched (this happens because kyanite consists of long, thin crystals). It has a specific gravity of 3.58. Kyanite is found in Brazil, Burma, Kenya, Europe, India, Australia, Kenya, and the USA. Kyanite's chemical composition is Al2SiO5; it is composed of andalusite and sillimanite.
London blue topaz London blue topaz (Aluminium silicate fluoride hydroxide) is the darkest blue variety of topaz. Most blue topaz is silver topaz that has been irradiated and heat treated, but some stones are blue naturally. London blue topaz is found in Brazil, U.S.A., Sri Lanka, Myanmar (Burma), Russia, Australia (including Tasmania), Pakistan, Mexico, Japan, and Africa. Topaz has a hardness of 8 and a specific gravity of 3.5-3.6.
Moissanite Moissanite is a very hard mineral that was discovered by Dr. Ferdinand Henri Moissan (1852-1907), a French chemist and Nobel Prize winner (Moissan did work on synthesizing diamonds and discovered carborundum in 1891). He found tiny amounts of Moissanite in the iron meteorite that was found at Diablo Canyon (also called Meteor Crater) in Arizona, USA. Moissanite ranges in color from colourless to blue to green to yellow. Its chemical makeup is Silicon Carbide (SiC); it is also called Carborundum. Moisannite crystals are transparent to translucent. Moissanite has a hardness of 9.25 (this is almost as hard as diamond) and a specific gravity of 3.1 - 3.2. Laboratory-grown Moissanite is sold as a gemstone.
Moldavite Moldavite is a rare, glassy, translucent, dark green gemstone. Moldavite is a silica-based tektite, a mineral formed when a meteorite (a rock from space) struck the Earth's surface and melted and fused the surrounding rock. Moldavite is only found in Bohemia (the Czech Republic) in the Ries Crater in the Moldau River valley (which it was named for). Moldavite was discovered in the late 1800's; the meteorite from which it formed hit the Earth about 14.7 million years ago. Moldavite has a hardness of 5.5-6.6. Inclusions of gas bubbles and iron/nickel spherules are common. This natural glass has been used for jewellery, religious articles, and decorative objects since prehistoric times.
Morganite Morganite is a transparent to translucent pink gemstone. It is a variety of beryl, Be3Al2(Si6O18) that contains some manganese (giving the stone its pink colour). Morganite has a hardness of 7.5 - 8 and a specific gravity of 2.71 - 2.90. It has poor cleavage and is brittle. Morganite is often heat treated to give the stone a purer pink color (and remove any yellow spots). Morganite was named for J. Pierpoint Morgan, the American industrialist and gem collector. Morganite is found in Brazil, Madagascar, Italy, Pakistan, Mozambique, Namibia, Zimbabwe, and the USA (California, Maine, Connecticut, and North Carolina).
Mystic fire (AKA Mystic Topaz) Mystic fire (also called mystic topaz or rainbow topaz) is topaz that has been colour enhanced by coating it with a fine layer of metal atoms (in a process called vacuum deposition). This stone has red, green, violet, and blue streaks. Mystic fire has a hardness of 8.
Obsidian Obsidian (also called Apache tears) is a volcanic glass that is usually black, but is occasionally red, brown, grey, green (rare), dark with "snowflakes," or even clear. This glassy, lustrous mineral is found in lava flows, and obsidian stones can be massive. Obsidian is formed when viscous lava (from volcano's) cools rapidly. Most obsidian is 70 percent silica. Obsidian has a hardness of 5 and a specific gravity of 2.35. The pin above is Mahogany (brown) obsidian.
Opal Opals are semi-precious stones that are luminous and iridescent, frequently with inclusions of many colours ("fire"). Opal is a mineral composed of noncrystalline (amorphous) silica (and some water) and is a species of quartz. There are three major types of opals: common opal, opalescent precious opal (white or black, with a rainbow-like iridescence caused by tiny crystals of cristobalite), and fire opal (a milky stone that is fiery orange to red in colour with no opalescence). Contra luz opals are transparent opals that show a brilliant play of iridescence only when light shines through the stone. Many opals have a high water content - they can dry out and crack if they are not cared for well (opals should be stored in damp cotton wool). Some opals are treated with oil, wax or resin to enhance their finish. Opals have a hardness of 5.5 to 6.5 and a specific gravity of 1.98-2.50. Opals are found in many places worldwide, including Kenya, Czechoslovakia, Brazil, Peru, Honduras, Mexico, Canada, and the USA -- but Australia has a tremendous variety of beautiful opals
Padparadscha Sapphire Padparadscha sapphires (also spelled padparadschah) are a rare pink-orange variety of corundum or the synthetic equivalent. These gems are mined in Sri Lanka and are usually heat treated to improve and intensify the color. The name padparadscha comes from the Sinhalese word for lotus flower. Hardness = 9, specific gravity = 4.
Peridot Peridot (also known as the "evening emerald" and chrysolite) is a yellow-green semi-precious stone with an oily luster; peridot is a transparent, green form of olivine. Peridot exhibits double refraction; when you look through the stone, things appear double. For example, when looking into a faceted peridot gemstone, the number of bottom facets appears to be double the actual number of facets. Most peridots are from a volcanic island in the Red Sea, Zebergit / St. John, the "Serpent Isle." Peridots have been found in meteorites. Peridot has a hardness of 6.5. Peridot cat's eye also exists.
Petrified wood Petrified wood (also called xyloid jasper or jasperized wood) is wood that has fossilized - all the original chemicals in the wood have been replaced with minerals, making a stone-like replica of the original wood.
Pink topaz Pink topaz (Aluminium silicate fluoride hydroxide) is a very hard pink gemstone. Pink topaz is usually created by irradiating common yellow topaz. Topaz has a hardness of 8 and a specific gravity of 3.5-3.6.
Prase opal Prase opal is a green, translucent opal that looks quite similar to chrysoprase (hence the name "prase") or jade. This type of opal is found in Tanzania, Africa. This gem does not display the iridescence found in some opals.
Pyrope garnet Pyrope garnet is the familiar deep red garnet. Red garnet is the birthstone for January. Garnet has a hardness of 6-8 and a specific gravity of 3.5 - 4.3. The formula for garnet is: A3B2 (SiO4) 3. Pyrope garnet is also called (misleadingly) American Ruby, Arizona Ruby, Australian Ruby, Bohemian Ruby, California Ruby, Cape Ruby, Colorado Ruby, Elie Ruby, Montana Ruby, and Rocky Mountain Ruby.
Purple diamond Purple diamonds are quite rare, fancy diamonds and are quite valuable. Diamonds are precious, lustrous gemstones made of highly compressed carbon; they are one of the hardest materials known. Diamonds have a hardness of 10, a specific gravity of 3.5, and a refractive index of 2.417 - 2.419.
Quartz Quartz is a crystalline mineral that come in many forms, including amethyst, aventurine, citrine, opal, rock crystal, tigers eye, rose quartz, and many others. Rutilated quartz and tourmalinated quartz have needle-like inclusions of other minerals. Quartz has a hardness of 7.0. This common mineral is found worldwide.
Rainbow topaz Rainbow topaz (also called mystic topaz or mystic fire) is enhanced that has been colour enhanced by coating it with a fine layer of metal atoms (in a process called vacuum deposition). This stone has red, green, violet, and blue streaks. Mystic fire has a hardness of 8.
Red beryl Red beryl is a is a rare, deep red variety of beryl. Gemstone-quality forms of this mineral are found in only one place in the world, in the Wah Wah Mountains, near Beaver, Utah, USA. Small crystals of this gem were first found in 1905 in the Thomas Range in Juab County, Utah. The mine bearing gemstone-quality red-beryl was found in the 1950's. The biggest red beryl crystal ever found was 14mm by 34mm, weighing about 54 carats. The average faceted red beryl gemstone weighs about 0.15 carats. Red beryl has a hardness of 7 - 8, a specific gravity of 2.66-2.70, and a refractive index of 1.564-1.574. The chemical formula Be3 Al2SiO6, with other trace elements. Internal flaws in beryl gems can be hidden by treating the stone with oil(this is often not disclosed to the buyer).
Red diamond Red diamonds are rare, fancy diamonds and are quite valuable. Diamonds are precious, lustrous gemstones made of highly compressed carbon; they are one of the hardest materials known. Diamonds have a hardness of 10, a specific gravity of 3.5, and a refractive index of 2.417 - 2.419.
Rhodochrosite Rhodochrosite is a mineral whose colour ranges from rose to pink to almost yellow or brown. Although it is very pretty, this stone is soft and brittle; it is used in jewellery and for carvings and figurines. Rhodochrosite is Manganese Carbonate; its chemical formula is MnCO3. Rhodochrosite has a hardness of 3.5 - 4.5 (glass has a hardness of 4) and a specific gravity of 3.5. Rhodochrosite is found in Argentina, Peru, Germany, Mexico, South Africa, Russia, Italy, USA (Colorado and Montana), and Romania. Rhodochrosite is not enhanced.
Rhodolite Rhodolite (meaning "rose stone" in Greek) is a purple-red to pink-red variety of garnet. It is a combination of almandine and pyrope (it is sometimes called pyrope-almandine garnet). This silicate stone has a hardness of 7-7.5 and a specific gravity of 3.5 - 4.3. The formula for garnet is: A3B2 (SiO4) 3. Rhodolite is found in the US, Zimbabwe, Kenya, and Sri Lanka (Ceylon). Rhodolite is not enhanced.
Rubellite Rubellite (sometimes spelled rubelite) is a red variety of tourmaline. Rubellite is red in both incandescent light and daylight, and is more valuable than other varieties of red tourmaline.
Rubellite has a hardness of 7-7.5 and a specific gravity of 3.02-3.25. Rubellite is sometimes treated with fillers to increase the clarity of the stone.
Ruby Rubies are precious stones and a member of the corundum family (Al2O3). Rubies range in color from the classic deep red to pink to purple to brown. Rubies are extremely hard; only diamonds are harder. During the renaissance, people thought that rubies could counteract poison. Laboratory-produced rubies were created in the 1890's; they are difficult to distinguish from natural rubies. The biggest ruby in the word is the Raviratna, which weighs 3,600 carats. Rubies have a hardness of 9 and a specific gravity of 3.9 - 4.1. Rubies are found in Afghanistan, Australia, Brazil, Cambodia, India, Myanmar (Burma), Malagasy Republic, Malawi, Pakistan, Sri Lanka (Ceylon), Tanzania, Thailand, United States (Montana and North Carolina), and Zimbabwe (Rhodesia).
Ruby spinel A ruby spinel (or spinel ruby) is deep red, transparent spinel (not a ruby).
Sapphire Sapphire is a precious gemstone (a type of corundum) that ranges in colour from blue to pink to yellow to green to white to purple (mauve sapphire) to pink-orange (padparadscha sapphire). Six-sided asterisms sometimes occur in star sapphires (caused by inclusions of tiny, thin, parallel needles of rutile). Sapphires are related to rubies. Sapphires were once thought to protect the wearer from poisonous creatures. Sapphire has a hardness of 9 and a specific gravity of 3.9 - 4.1. Sapphires are often heat treated to improve their colour.
Sillimanite Sillimanite (aluminium silicate, Al2 SiO5) is a transparent to translucent mineral that ranges in colour from white to gray to brownish to greenish. Sillimanite has the same chemical formula as both kyanite and andalusite (these three minerals are polymorphs); Sillimanite is the rarest of the three (all three are used in high-temperature ceramics, used in spark plugs). Sillimanite has a hardness of 7.5 and a specific gravity of 3.2. Sillimanite is the state mineral of Delaware (since March 24, 1977); SIllimanite is found near Wilmington, Delaware. Sillimanite is found in Brazil, New England (USA), and Europe; it is found in areas of high-grade metamorphic rock.
Smoky quartz Smoky quartz is a type of brownish quartz that has a smoky look.
Snowflake obsidian Snowflake obsidian (also called flowering obsidian) is a volcanic glass that is usually dark (black or brownish) with white "snowflakes". This glassy, lustrous mineral is found in lava flows, and obsidian stones can be massive. Obsidian is formed when viscous lava (from volcano's) cools rapidly. Most obsidian is 70 percent silica. Obsidian has a hardness of 5 and a specific gravity of 2.35.
Spessartine garnet Spessartine garnet (also called Spessartite garnet) is a type of a garnet that is orange (it varies from reddish orange to brownish orange to yellowish orange). The chemical composition is Manganese Aluminium Silicate. Crystals vary from transparent to translucent. This relatively rare gem is found in Sri Lanka, Australia, Madagascar, Brazil, Sweden, Myanmar, and the U.S. Spessartine garnet has a hardness of 7.0 - 7.5, a specific gravity of 4.19 (relatively heavy), and a refractive index of 1.8.
Spinel Spinel is a very hard semi-precious stone composed of octahedral crystals. Spinel ranges in colour from red to black to yellow, frequently resembling rubies. Iron and chrome are components of spinel, giving it its colour. Spinel belongs to the feldspar species and is found in in Burma, Sri Lanka and Thailand. Some varieties include: Balas ruby (red spinel), Almandine spinel (purple-red), Rubicelle (orange), Sapphire spinel (blue), Ghanospinel (blue), Chlorspinel (green). Spinel is also laboratory synthesized. Spinel has a hardness of 8, a specific gravity of 3.58-4.06, and a refractive index of 1.72.
Sphene Sphene (sometimes called titanite) is a mineral that comes in green, yellow, white, brown or black wedge-shaped crystals (sphene means wedge in Greek). Sphene is used only rarely as a gem (due to its relative softness). It's chemical formula is CaTiSiO5, Calcium Titanium Silicate. Sphene has a hardness of 5-5.5, a specific gravity of 3.3 - 3.6, and a white streak.
Star ruby A "star ruby" is a ruby that exhibits an asterism, a six-pointed star of light (when cut as a cabochon). The world's biggest star ruby is the Rajaratna, which weighs 2,475 carats. The world's biggest double-star ruby (with a 12-pointed star) is the Neelanjali, weighing 1,370 carats. Most star rubies today are synthetic.
Sugilite Sugilite is a medium to dark purple semi-precious gemstone (it can also range from pink to brown to black). It is usually opaque with a waxy lustre (but can be translucent) and often has brown, pink and white inclusions, looking like a purple version of turquoise. It is usually polished and not faceted. Sugilite has a hardness of 5.5-6.5 and a specific gravity of 2.75 - 2.80. This stone is not enhanced - massive stones are often found. Sugilite is Potassium Sodium Lithium Iron Manganese Aluminium Silicate; its formula is KNa2Li3(Fe, Mn, Al)2Si12O30. This stone was named for Ken-ichi Sugi, the Japanese geologist who discovered it in 1944. It is found in Iwagi Island, Shikoku, Japan and Mont Saint-Hilaire, Quebec, Canada, but the largest deposits are in northern South Africa.
Sunstone Sunstone is also called aventurine feldspar (a variety of oligoclase). This gemstone varies from golden to orange to red-brown, and can be transparent or translucent. Sunstone is metallic looking due to sparkling red, orange or green crystalline inclusions (these are hematite or goethite crystals). Sunstone is found in Canada, the USA (in Oregon), India, Norway, and Russia. This brittle stone has a hardness of 6 and a specific gravity of 2.63 - 2.67. Sunstone is not enhanced.
Tanvorite Tanvorite is a trademarked name for a manmade gemstone. This synthetic stone is a deep blue-purple stone that resembles tanzanite.
Tanzanite Tanzanite (strontium-rich Calcium-aluminium silicate) is a valuable, transparent, blue-violet type of zoisite resembling sapphire. Tanzanite has a hardness of 6 and a specific gravity of 3.35. It is often heat treated in order to produce a deeper blue-violet colour. This mineral was discovered in 1967 by Manuel d' Souza (an Indian tailor) southwest of Mt. Kilimanjaro in Tanzania, Africa.
Topaz Topaz (aluminium silicate fluoride hydroxide) is a very hard gemstone that ranges in colour from brown, to yellow to blue to pink. Pink topaz is usually created by irradiating common yellow topaz. Other colours are often created by heat treating and/or irradiating topaz. Imperial topaz is golden orange-yellow topaz; it is the most valuable topaz. Topaz has a hardness of 8 and a specific gravity of 3.5-3.6. Topaz may have been named for the legendary Topasos Island in the Red Sea.
Tiger's eye Tiger's eye is a yellowish-brown to reddish-brown gemstone that has a silky luster. This gemstone has bands of yellow and brown; when viewed from the opposite direction, the colours are reversed. Tiger's eye is usually highly polished and set as a cabochon (or cut as a bead) to display the stone's chatoyancy (light reflected in thin bands within the stone). Tiger's eye is a type of chatoyant quartz with fibrous inclusions (especially crocidolite). This stone is sometimes heat-treated. Tiger's eye has a hardness of 7.0. Most tiger's eye is mined in South Africa, but it is also found in Australia, Brazil, Burma (Myanmar), India, Namibia, Sri Lanka (Ceylon), and the USA. Green-grey varieties ofthis stone are called cat's-eye quartz. Blue-grey to bluish varieties are called hawk's-eye. Deep brown varieties of this stone are called bull's-eye or ox-eye.
Tourmaline Tourmaline is a dichroic gemstone that comes in many, many different colours; it also appears to have different colours depending on the angle at which it is seen. Tourmaline has the greatest colour range of any gemstone - the lighter colours are more valuable than the darker colours. It ranges in colour from pink to green to red (rubellite) to purple to blue-green (indicolite) to colourless (achroite) to black.
Watermelon tourmaline is a tourmaline gemstone that is multicoloured, going from pink to green. and is both pink and green. Tourmaline occurs as an elongate three-sided prism and is mined in Brazil, The Ural mountains in Russia, Namibia, Sri Lanka, and California. Tourmaline was only discovered in the 1700's. Tourmaline has a hardness of 7-7.5 and a specific gravity of 3.02-3.25. It is doubly-refractive.
Tourmalinated quartz Tourmalinated quartz is a variety of transparent quartz that has needle-like inclusions of black to dark green tourmaline crystals. This beautiful stone is found worldwide. Tourmalinated quartz has a hardness of 7.0. This stone is not enhanced.
Tsavorite Tsavorite is a rare, deep green variety of grossular garnet, a type of garnet, calcium-aluminium silicate. The emerald green colour comes from vanadium and chromium. Tsavorite is similar to emerald, but is rarer and more durable; it also has a higher refractive index, 1.74. Tsavorite stones over two carats are considered large and are very rare. Tsavorite has a hardness of 7.5 and a specific gravity of 3.6. Tsavorite is found in east Africa; it was named by Harry B. Platt of Tiffany & Co. for the Tsavo National Park in Kenya, where this gemstone was originally found in 1967. Tsavorite is not enhanced.
Turquoise Turquoise is a non-translucent, porous semi-precious stone (it is a hydrated phosphate of copper and aluminum) that is usually cut as a cabochon. Turquoise was believed to have been first found in Turkey, hence its name (Turquie is the French word for Turkey). The oldest turquoise mines are located in Alimersai Mountain in Persia (Iran) and in the Sinai Peninsula in Egypt. Turquoise is found in desert regions worldwide. The finest turquoise is Persian (Iranian) turquoise; it is robin's egg blue and has no matrix (streaks of the mother stone from which they were found). North American turquoise is greener and has a matrix streaks. Over the years, oil from your skin is absorbed by the stone and it will change colour slightly. Turquoise has a hardness of 6 and a specific gravity of 2.60-2.85. Turquoise is the national gemstone of Iran.
Unakite Unakite is an opaque mineral that is green with patches of red and pink. Unakite is a variety of granite that contains green epidote and pink feldspar (but lacks mica). It has a hardness of 6 to 7 and a specific gravity of 2.86 - 3.2. Unakite was named for the Unaka Mountains Mountains in Tennessee, USA. Unakite is found in the USA and Africa.
"Water Sapphire" "Water sapphire" is not a true sapphire, but is iolite, a more common, softer, and much less expensive mineral. It is a transparent, violet-blue, light blue, or yellow-grey mineral. Iolite is pleochroic; a single stone will show many colours (in the case of Iolite, violet-blue, light blue, and yellow-grey). Iolite has a hardness of 7 - 7.5. Iolite is found in Sri Lanka, India, Madagascar and Burma.
YAG YAG is an actonym for yttrium aluminium garnet, a man-made imitation diamond. This imitation stone lacks the fire of a natural diamond.
Zircon Zircon (zircon silicate) is a lustrous gemstone that comes in colours ranging from golden brown to red to violet to blue. Pure zircon is colourless, but most zircon stones are brown. Zircon stones can be heat-treated to become blue or colourless; sometimes, heat-treated stones revert to their original colour. Clear zircon is sometimes sold (intentionally or otherwise) as diamond. It has a hardness of 7.5 and a specific gravity of 3.90-4.71.
