Description
The mineral turquoise is a hydrated copper-aluminum-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 luster and a pale blue-white streak color. The crystal system is triclinic and the cleavage is perfect along the crystal plane [001] and good along [010]; however, 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 it passed through when the mineral first reached Europe; however, as far as is known, it does not occur in Turkey. 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. The mineral was also mined in the Sinai, and in Serabit el-Khadim there is a temple dedicated to the Egyptian “Lady of Turquoise” (the goddess Hathor). Turquoise is used as a semi-precious stone. During the Ottoman Empire, turquoise was exported as a precious mineral, especially to Persia. Currently, turquoise is mined in Mexico, the United States, and China. Imitation turquoise was first produced in France in 1972, but the properties of this imitation differ from those of the natural varieties. Nevertheless, the best-selling turquoise today is synthetic.
