Copper and aluminum phosphate with colours from pale blue to green and used a gem since Antiquity. Turquoise, a rarely crystallised stone, is found as a compact mass or sometimes in small veins, encrusting or as stalactites. It is usually found in magmatic rock. The main deposits are located in Tibet, Iran, Uzbekistan, Poland, Chile and the US. 
The name ‘turquoise’ derives from the old French "turcois", as the gem trade was done through Turkey for a considerable period in history. In America the Hopi and Navajo Indians often used it to make tribal Jewellery.