Dioptase (CuSiO3·H2O) is an intense emerald-green to bluish-green copper cyclosilicate mineral. It forms very distinctive, well-developed transparent to translucent crystals, although only a handful of well-known deposits have produced large crystals. Dioptase has a hardness of 5, the same as tooth enamel. Crystals are generally fragile and can easily break or crumble. This mineral was named in 1797 from a combination of the Greek words Dia, which means "through" and Optasia, which means "to see".
The type locality for Dioptase, known for producing large and exceptional crystals, is Altyn-Tyube, Kazakhstan. However, the most famous locality is certainly Tsumeb in Namibia, which has produced outstanding specimens over the years. The copper mines of the Kaokoveld District in Namibia are also worth mentioning, as well as the Katanga Copper Crescent in Democratic Republic of Congo.