PRECIOUS STONES. A substance to be precious must possess variety, beauty, durability and portability. Precious stones, phenomenal stones and semi-precious stones are such as may be used for ornamental jewelry. Strictly speak ing the term precious stone is reserved to desig nate the diamond, the ruby, the sapphire and the emerald, the others being called "phenomenal and "semi-precious," but the designation "precious° has been loosely used to indicate all stones used for the jeweling of choice objects of adornment. The following are those which chiefly claim attention : See the special article describ ing this gem.
Spodumene has a hardness of 6.5 — 7, and a specific gravity of 3.13— 3.19. The rich green variety, hiddenite, named after the late William Earle Hidden, was found at Stony Point (now named Hiddenite). Alexander County, N. C., in crystals furnishing gems weighing up to five carats each. A yel low variety which occurs in Brazil is called triphane. Kunzile (q.v.) is a rich, lilac-hued variety of spodumene, of which fine examples come from Pala, San Diego County, Cal., It also occurs in crystals weighing up to 100 carats in Madagascar. Spodumene was at an earlier time called "triphane," a name given it by the great crystallographer Hatiy.
Titanite (or sphene) is a calcium silico titanite, having a hardness of 5.5 and a specific gravity of 3.5. It furnishes the most brilliant yellow and brown gem except the diamond. Fine examples have been found in Bridgewater, Bucks County, Pa., from which gems weighing from 10 to 20 carats could be cut. Other sources are the Tilly Foster Mine. New York, and the Pfitschtal and Zillertal, in A name given to a hydrocarbon assumed to be present in certain diamonds, namely those which on that account exhibit fluorescence and phosphorescence. The sub stance apparently has a bluish-white color. The blue white diamonds of Brazil are called Tiffanyite diamonds.* A natural carborundum, a car bon silicide, of which the French chemist, Henri Moissan, found, in 1905, small blue or bluish green crystals in the meteorite of Cafion Diablo, Arizona, in association with microscopic dia monds. It belongs to the rhombohedral division
of the hexagonal system. The cleavage is poor; the fracture conchoidal; the hardness is next to that of the diamond. The refractive indices are higher than 1.75. As many as 44 varieties of the crystal forms have been observed. The name was given in honor of the discovered' Rubies and The ruby and the sapphire are transparent varieties of corundum (q.v.), the first being carmine-red, and the sec ond bright blue and velvet blue. Other colors also occur, as yellow, green and purple, called, respectively, Oriental topaz, Oriental emerald and Oriental amethyst. Corundum crystallizes in the hexagonal system, and consists of alumina nearly pure. In hardness it ranks next below the diamond, being rated as nine on the scale. The finest rubies are found in Burma, in the Mogok Valley, northeast of Mandelay. They are also mined in Siam, where they are of a darker shade, and in Ceylon, where they are of lighter hue and often of great brilliancy. The finest Burmese rubies have a peculiar tint, called 'pigeon's blood." Rubies of large size are extremely rare, and when they weigh four carats or more they are worth from two to five, and formerly 10 times the price of dia monds of the same size. Sapphires come prin cipally from Ceylon, Cashmere and Siam, the finest tints being known as the and the °velvet blue.° In Australia, especially at Anakie in Queensland, many dark-blue sap phires are found, too deep in hue to be of value if cut into large gems, so they are gen erally cut as calibre or small stones. Queens land has furnished some wonderful golden yellow corundums, these being the centres of blue crystals. Sapphires are also found in Montana at several points, generally under two carats each; the choicest are mined at Yogo Gulch, in Fergus County. These are of a rich blue color. Other mines are at Rock Creek, Granite County, where there is a great variety of shades; examples also occur at Cottonwood Creek, and along the bars of the Missouri River, not far from Helena, Mont. Fancy colors are of little value compared to the blue.