Turquoise is a hydrous copper-aluminum phosphate, CuAl6(PO4)4(OH)8·4H2O, that forms by near-surface alteration of igneous rocks rich in aluminum. Turquoise comes from the French word for Turkish, sometimes called Turkey stone. Its color ranges from yellowish green to sky blue. Blue turquoise is second only to jade in value among the nontransparent gemstones. This specimen displays the botryoidal habit that turquoise commonly has. Turquoise is the state gem of Arizona, Nevada and New Mexico.
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