Turquoise << TUR koyz or TUR kwoyz >> is a mineral widely used as a gemstone. It is prized for its color, which ranges from sky-blue to blue-green or yellow-green. Turquoise is relatively soft, and so it is easy to shape and polish. It has a dull, waxy luster and is nearly opaque (nontransparent). Turquoise consists chiefly of a hydrous aluminum phosphate, a compound in which aluminum and phosphorus are chemically combined with water. It also contains copper, which gives it its bluish color.
Turquoise occurs in arid regions. It is formed when surface rocks that are rich in aluminum undergo a chemical change. In most cases, turquoise results from the weathering of lava. Major deposits of turquoise are found in Iran and Tibet. Large amounts of the mineral also occur in the Southwestern United States, especially in Nevada and New Mexico.
People have used turquoise for jewelry and other decorative purposes since ancient times. It is one of the December birthstones (see Birthstone). The demand for turquoise remains so great that artificial varieties of the stone are produced.
