Gemstones

Gemstones were formerly classed as precious, semiprecious, and ornamental stones. Today this classification is largely replaced by the broader term gem materials. The following list includes the major gem materials and some of the less important ones.

Achroite. A colorless variety of tourmaline.
Agate. A type of chalcedony, with colored bands, first found on the banks of the river Achates hence the name agate. The markings of moss agates occasionally resemble natural objects and so were much prized in the past. Most agates are naturally grayish and are artificially colored. They are usually soaked in solutions of sugar or honey and acid or salt solutions and then heated.
Alexandrite. Named after Alexander II of Russia. A variety of chrysoberyl, grass green in color. Shows a red hue in artificial light.
Amazonite, or amazonstone. A feldspar, jadelike in color. Found in Canada, Brazil, Russia (Ural Mountains), Tanzania, Madagascar, Virginia, and Colorado.
Amethyst. A transparent violet to purple quartz. Believed by the ancient Greeks to prevent intoxication. Amethysts were used in both Greek and Roman jewelry. Under certain conditions the color of some amethysts may be improved by heating. Under other conditions heating may turn them yellow, then clear. Found in quantity in southern Brazil and northern Uruguay. Smaller amounts come from India, Sri Lanka, and Madagascar.
Aquamarine. Transparent sea blue or sea green beryl; of the same family as the emerald but far less valuable. Found in many parts of the world, particularly Brazil, Sri Lanka, India, and Madagascar, and in Maine, New Hampshire, Connecticut, and North Carolina. An aquamarine crystal found in Brazil in 1910 weighed about 240 pounds (110 kilograms).
Aventurine. A quartz spangled with yellow mica or other mineral. Imitation aventurine is called goldstone.
Azurite. An azure blue copper carbonate found in most copper mines. Pliny called it caeruleum, which is Latin for “like the sky.” Used for coloring tabletops, vases, and jewelry. Found in Namibia, France, Chile, the Democratic Republic of the Congo, Arizona, Utah, and Montana.
Beryl. A silicate occurring in several forms. Includes the emerald, aquamarine, golden beryl, morganite, and goshenite.
Bloodstone, or heliotrope. A dark green chalcedony (quartz) spotted with red jasper. Prized in the Middle Ages for carvings of martyrs, with the red flecks representing blood spots. Was called St. Stephen's Stone. Widely used in signet rings, cuff links, tiepins. Found in the Ural Mountains, India, and the western United States.
Cairngorm. A smoky yellow to smoky brown quartz, readily decolorized by heating. Very popular in Scotland, it is sometimes called Scotch topaz. Used for pins, brooches, and similar jewelry.
Carbuncle. A garnet cut en cabochon; that is, flat on the bottom, rounded above, without facets. In ancient times any red stone was called a carbuncle, and a mythical “carbuncle” was said to give out light in darkness.
Carnelian, or sard. Name given to orange red chalcedony. Used for ornamental carvings. Chief sources are Australia, India, and Brazil.
Cat's eye. The cheaper cat's eye is of quartz, the more highly valued is of chrysoberyl. Colors range from apple green to olive, from yellow to brown, but each color has a streak or line through the middle, of varying brilliance, like a cat's eye. Found in Sri Lanka, India, Brazil, and Bavaria.
Chalcedony. A cryptocrystalline quartz, used by gem engravers since ancient times. The Bible has many references to it. Color usually white, pale blue, or gray. Varieties include carnelian, or sard; chrysoprase; prase; plasma; bloodstone, or heliotrope; agate; onyx; sardonyx; and jasper. Used chiefly for ornamental carvings. Widely distributed. Excellent stones are obtained from the Ural Mountains, Uruguay, and Romania.
Chrysoberyl. A rare, unusually hard stone. One variety, the alexandrite, green by day and red by lamplight, had a great vogue among aristocrats of czarist Russia. Other varieties include chrysolite and cat's eye.
Chrysolite. An olive green vitreous magnesium iron silicate, also called olivine and peridot. It is crystalline and, when transparent, used as a gem.
Chrysoprase. An apple green type of chalcedony.
Citrine. A clear yellow quartz resembling topaz. Used for pendants, bracelets, earrings, and pins.
Coral. Precious coral is red and branching, found in the Mediterranean. Black coral has been found in the Persian Gulf and on the Great Barrier Reef off Australia.
Diamond. Pure crystallized carbon, the most highly esteemed of all gemstones.
Emerald. A deep green brilliant emerald is one of the costliest of gems. The emerald is a variety of beryl. The finest stones come from Colombia. Other sources are Brazil, Egypt, Australia, Austria, Norway, and North Carolina.
Feldspar. Silicate feldspar produces several gemstones: amazonite, a bright green; moonstone, opalescent; sunstone, reddish; labradorite, gray with play of colors in blue and green and sometimes yellow or red. Feldspars are widely distributed.
Garnet. A gem, usually deep red, of several varieties, including the almandite and pyrope. When cut en cabochon garnets are called carbuncles. Garnet is found in nearly all colors but blue. Rarest of garnets is the green demantoid, found only in the Ural Mountains. Others come from the Czech Republic, Brazil, India, Sri Lanka, and the United States.
Girasol. A variety of opal. Iridescent.
Heliotrope. Same as bloodstone.
Hematite. Black crystalline iron; when finely divided, streaked with red. Popular for costume jewelry. Found in England, Norway, Sweden, the island of Elba, and the Lake Superior region.
Hyacinth, or jacinth. Variety of zircon.
Jade. A name applied to jadeite and nephrite. The color is usually green but sometimes a whitish cast appears. The stone takes a high polish. Jewelry, cups, and bells are made of it, and poems of Chinese emperors have been carved in priceless jade bowls. In China jade is considered the most precious gemstone.
Jasper. An opaque ornamental chalcedony, in red, yellow, brown, green, or gray blue, used for vases, tables, mantels, and pillars. Jasper is often striped. Swiss or German lapis is jasper artificially colored.
Jet. A hard, black lignite, a variety of coal. Takes high polish. Popular for ornaments and costume jewelry. Many jet articles manufactured in Yorkshire, England, from local lignite and imports from Spain. Pennsylvania anthracite and Scottish cannel coal are often used in place of jet.
Labradorite. A pearl gray or brown feldspar, showing many colors in light. Takes high polish.
Lapis lazuli. The blue mineral lazurite. Mines in Afghanistan, worked for 6,000 years, probably world's oldest mines. Called “sapphire” by ancient world. Also found in Chile, Siberia, and southern California. Used for jewelry, mosaics, inlaid work, vases.
Malachite. A green copper carbonate; used for making ornaments.
Marcasite. Differs from pyrite only in crystal structure; often set as brilliants in costume jewelry.
Moonstone. A milky, translucent feldspar. The finest specimens are found in Sri Lanka.
Morganite. A rose colored beryl. Named for J. Pierpont Morgan.
Obsidian. A smoky natural glass of volcanic formation, abundant in Yellowstone National Park.
Olivine. A silicate of iron and magnesium. Bottlegreen variety best; others are peridot and chrysolite.
Onyx. The cameo carver's favorite material, chalcedony, with horizontal stripes of black and white. Also used for tabletops, lamps, and decorations
Opal. Noncrystalline silica, often combining several colors and frequently opalescent .
Pearl. Not a true gemstone.
Peridot. A yellowish green olivine. Found in St. John's Island (Red Sea), Australia, Arizona, Hawaii, and, rarely, other places.
Plasma. A variety of green chalcedony.
Prase. A dull green chalcedony.
Pyrite. A pale yellow opaque iron disulfide.
Pyrope. A variety of garnet, often deep red.
Quartz. Crystalline silica, the most common of all minerals. Gem varieties include rock crystal, amethyst, citrine, siderite, aventurine, chalcedony, cat's eye, and rose, smoky, milky, and rutilated quartz.
Rhinestone, or brilliant. Imitation gem made from special kinds of glass called paste, or strass. Colorless, sparkling, in imitation of diamonds. Rhinestone glass made from heating mixture of quartz, red lead, potassium carbonate, borax, white arsenic.
Rhodolite. A pink or purple variety of pyrope.
Rock crystal. A clear quartz much used for beads, vases, goblets, and crystal balls.
Ruby. A transparent red corundum valued according to shade of color. Large rubies are often worth more than fine diamonds of the same size. Pigeon blood (deep carmine red) rubies, which seldom exceed three carats, are obtained from Myanmar. Darker rubies come from Thailand. Rubies also occur in Sri Lanka, Afghanistan, and North Carolina.
Sapphire. A transparent corundum, or aluminum oxide. Sapphires range from white through blue, violet, yellow, and green to near black. Blue star sapphires with six rays are favorite stones. Fine sapphires are equal in value to diamonds of equal size. Found in Myanmar, Thailand, Sri Lanka, and Jammu and Kashmir.
Sardonyx. A variety of onyx with parallel layers of white, brown, black, and red sard. Used in cameos and intaglios. Chief sources are Brazil, Uruguay, Madagascar, India, and Texas.
Spinel. A red, violet, blue, green, or yellow magnesium aluminate. Sometimes called “mother of ruby.” Found in Myanmar, Thailand, and Sri Lanka.
Sunstone. A reddish feldspar with fiery reflections.
Tigereye. Like cat's eye, a chatoyant stone; that is, when polished, the interior shows an undulating light.
Topaz. An aluminum fluosilicate occurring in tawny yellow, blue, green, reddish violet, pink, and colorless varieties. Found in Brazil, Siberia, Sri Lanka, and the United States.
Tourmaline. A complex aluminum borosilicate occurring in great variety colorless, rose red, green, blue, yellowish, green, honey yellow, violet, and dark blue. Most tourmaline is obtained from Brazil, Elba, Madagascar, and Maine, Connecticut, and California.
Turquoise. A hydrous copper aluminum phosphate ranging from sky blue to greenish gray. Often cut en cabochon. Widely used for bracelets, earrings, pins, belt buckles, and saddle studdings. Faded by heat and sunlight. Found in Iran, New Mexico, and Nevada.
Zircon. A zirconium silicate usually occurring in brownish, gray, or brownish red varieties, but sometimes in yellows and greens. Colorless and blue varieties are usually produced by heating brown zircons. Zircons come chiefly from Sri Lanka and Indochina, though Myanmar, Australia, and New Zealand are also good sources.