Tennantite

Tennantite is a copper arsenic sulfide mineral with the formula Cu12As4S13. It represents the arsenic-rich end member of the tetrahedrite-tennantite solid-solution series, the antimony-rich end member being tetrahedrite (Cu12Sb4S13). The two minerals share a complex sulfosalt structure and can form complete solid solutions between arsenic and antimony.

Tennantite crystallizes in the isometric (cubic) system. Crystals are rare and it more commonly occurs as granular, massive, or prismatic aggregates with a metallic luster. The color ranges from steel-gray to black, the streak is gray to black, and the mineral is opaque. Mohs hardness is about 3.5–4.

In nature, tennantite forms in hydrothermal veins and in copper-bearing skarns and replacement deposits. It is widely distributed in ore districts worldwide and is commonly associated with quartz, calcite, sphalerite, galena, chalcopyrite, bornite, and other copper sulfides and sulfosalts.

The mineral was named after James Tennant, a British mineralogist, in connection with its occurrence at the Tennant mine in Cornwall.

Uses and hazards: Tennantite is an ore of copper, but its arsenic content makes its handling and processing hazardous; it is not typically a primary copper ore where higher-grade minerals are available. Specimens are valued by mineral collectors and used for study of sulfosalt minerals.