tetrahedrites

Tetrahedrites are a group of copper sulfosalt minerals with the general formula (Cu,Fe)12Sb4S13. They are characterized by their tetrahedrally coordinated copper atoms and their cubic crystal structure. The most common member of the group is tetrahedrite-Cu, which contains very little iron. Other members include tennantite-Cu (where arsenic replaces antimony), schwazite-(Y) (containing rare earths), and bismutotetrahedrite-Cu (with bismuth). These minerals are typically found in hydrothermal veins and are associated with other copper minerals like chalcopyrite and bornite. Tetrahedrites are opaque, metallic, and have a dark gray to black streak. They are relatively soft, with a Mohs hardness of 3 to 3.5. Geologically, tetrahedrites are considered minor ore minerals of copper and sometimes silver and mercury. Their importance also lies in their complex crystal chemistry, which has been a subject of scientific study.