Turquoise - CuAl₆(PO₄)₄(OH)₈·4H₂O

Habit: Sky blue, bluish green, apple green or green gray when massive; bright blue as crystals. Crystals rare, short and prismatic; normally massive, also cryptocrystalline, stalactitic, concretionary or as crusts or veinlets. Waxy luster, but vitreous as crystals; opaque, but transparent as crystals. Pale bluish streak.

Environment: A secondary mineral found with chalcedony, iron oxides, kaolin and oxyhydroxides in the potassic alteration zone of hydrothermal copper deposits. Also occurs as a vein-filling mineral in volcanic rocks and phosphate-rich sediments.

Etymology: From Turquie, the French name for Turkey, as turquoise from Iran was imported to Europe from there.