Turquoise from Bahia, Brazil.

The mineral turquoise is a hydrated copper-aluminium phosphate with the chemical formula CuAl6(PO4)4(OH)8 4(H2O). The green, yellow-gray, light blue, but typically blue-green turquoise has a waxy sheen and a pale blue-white stripe color. The crystal system is triclinic and the cleavage is perfect according to the crystal plane [001] and good according to [010]; moreover, it occurs almost exclusively in cryptocrystalline forms, so the cleavage is not observable in practice. The average density is 2.7 and the hardness is 5 to 6. Turquoise is not radioactive. The mineral turquoise is named after Turkey, the country through which it passed when the mineral first reached Europe; moreover, it does not occur in Turkey as far as is known. The color turquoise is named after this mineral. Turquoise is mainly found as a secondary mineral in copper ores. The type locality is the Nishapur deposit in Iran. The mineral was also mined in the Sinai and in Serabit el-Khadim there is a temple dedicated to the Egyptian "Lady of Torquoise", (the goddess Hathor). Turquoise is used as a semi-precious stone. During the Ottoman Empire, turquoise was exported as a precious mineral, mainly to Persia. Today, turquoise is mined in Mexico, the United States, China, and Iran. Imitation turquoise was first produced in France in 1972, but its properties differ from those of natural varieties. However, the most commonly sold turquoise is now synthetic.