Turquoise is a sky-blue or green translucent to opaque basic aluminum phosphate that contains copper. It has been prized as a gemstone for millennia. Turquoise can be identified by its distinctive sky blue, blue-green or apple-green color and waxy to matt luster. Turquoise is the only gemstone that has a color named after it. Turquoise is sometimes mixed with malachite or chrysocolla, which causes a blue and green mottled appearance. The turquoise that is found in the USA contains iron rather than aluminum, so it is actually a mixture of turquoise and chalcosiderite. Since it contains iron, it is a green color. Pure blue turquoise is rare and turquoise is mostly interspersed by brown, dark-grey or black veins, which can be sparse or dense. Turquoise is translucent to opaque, though translucent materials are rare. It exhibits a waxy to matt luster. Most turquoise has dark-grey, brown or black veiny inclusions of matrix or other minerals.