Tcrquoise, a native hydrated phosphate of aluminum, found in the mountains near Nishapur, in Khorasan, Persia, and much valued as a gem. It is called by the Persians birusa, and is probably the callais of Pliny. An inferior variety is also found at Jordansmuhle in Silesia, and at Oelsnitz in Saxony. Major Macdonald discovered in Arabia Petraea, near Mt. Sinai, a variety of turquoise in a layer of red sandstone; it is darker and said to be of a finer blue than the Persian turquoise, but unfortunately it changes color, especially under the wheel of the lapidary. Persian turquoise has the chemical composition represented by the formula 2A1203,P206,5H20; it is uniform and stalactitic in structure, of hardness 6 on a scale of 10; sp. gr. 2.6 to 2.8; color a peculiar bluish green to azure-blue and white, slightly translucent to opaque, with small conchoidal fracture. Specimens of a fine blue are much the most highly prized. "When heated, the turquoise decrepitates strongly, gives off water, and, if colored, turns black. It tinges the blowpipe flame green, and with fluxes gives reactions of iron and copper. An analysis by Hermann of a blue oriental turquoise gave 28.9 of phosphoric anhydride, 47.45 alumina, 2.02 cupric oxide, 1.1 ferric oxide, 0.5 manganic oxide, 1.85 lime, and 18.18 water.

The turquoise is much used in oriental countries for ornamenting harness, girdles, swords, amulets, and charms, and is believed to have the power of protecting its wearer against contagion, or, when he is affected with disease, of changing color and becoming pale. Several antique cameos and intaglios cut in turquoise are in the Vatican at Rome. Fragments of the gem, which appear to have been parts of amulets, are often met with in Egyptian ruins. The shah of Persia is supposed to have in his possession all the finest gems in existence, as only those of inferior quality are allowed to be taken away.