Dioptase on calcite

This specimen shows a group of well-shaped rhombohedral pearly white calcite crystals with a liberal scattering of sugary emerald-green dioptase crystals. Dioptase is an uncommon copper mineral prized for its intense green colour. It is found in only a few copper mines world-wide, but the best examples come from Tsumeb, Namibia.

The Tsumeb Mine was unusual as it had two gossan zones, one at the surface and one hidden at depth. Groundwater, following a weakness in the rocks, was able to attack the primary ore 600 m below the surface, forming the second gossan zone. This lead-zinc sulphide deposit with veins of copper ore was first mined in 1906. The deep gossan zone contained over 130 different minerals, including some of the most spectacular specimens ever discovered. Albert Chapman purchased this specimen from a South African collector in the 1980s.

Tantara Mine, Katanga, Democratic Republic of the Congo (Zaire). 6 x 4 x 3.3 cm. D.50696. Albert Chapman Collection.