TURQUOISE. A bluish-green or greenish-gray mineral used in jewelry. It is a basic hydrous phosphate of aluminum and copper, rather brittle and with a hardness similar to that of iron. Turqouise is a mineral of secondary origin, occurring in thin veins, as patchy deposits or as encrustations in seams of rock that have undergone extensive alteration. The highly prized oriental turquoise occurs in much broken rock, together with secondary iron oxides, in Persia. It also occurs on the Sinai Peninsula in the Wady Maghara and S of Samarkand, Turkestan.