Dioptase from Tsumeb. (pieces of 150-400gr) The mine has been closed since 1985.

Dioptase is a copper-silicate mineral with the chemical formula CuSiO2(OH)2 and belongs to the cyclosilicates. This mineral, which varies from transparent to translucent and has colors from dark blue-green to emerald green or turquoise, has a glassy luster and a green stripe color. The cleavage is good according to the crystal plane [1011] and it belongs to the trigonal crystal system. With an average density of 3.31, a hardness of 5 and non-radioactive properties, dioptase is a remarkable mineral. It has a birefringence of 0.0510 to 0.0530. The name is taken from the Greek words 'dia' (through) and 'optamai' (sight). As a secondary mineral, dioptase occurs in oxidized copper ore deposits, known sites at Tsumeb and Cochab in Namibia, and Altyn Tube in Kazakhstan. It is also found in the Christmas mine in Gila County, Arizona, USA. Dioptase is highly sought after by mineral collectors, but has no commercial applications beyond that. Although it is beautiful enough to serve as a gemstone, it is not hard and strong enough, so it is rarely cut as such.