Tetrahedrite

Tetrahedrite is a copper antimony sulfide mineral with the chemical formula Cu12Sb4S13. It belongs to the sulfosalt group and forms a solid solution with the arsenic-bearing member tennantite (Cu12As4S13); substitutions by zinc or iron produce additional members of the tetrahedrite group, such as tetrahedrite-(Zn) and tetrahedrite-(Fe).

Crystallography and appearance: Tetrahedrite crystallizes in the isometric (cubic) system and commonly forms well-developed crystals as well as massive, granular aggregates. Crystals are often tabular or dodecahedral in habit. The mineral is metallic in luster, with a steel-gray to black color and a gray streak. Mohs hardness is about 3.5 to 4, and the specific gravity typically ranges from about 4.3 to 4.8.

Formation and occurrence: Tetrahedrite occurs in hydrothermal veins and as disseminated replacements in sulfide-rich environments. It is frequently associated with quartz, calcite, sphalerite, galena, pyrite, and bornite. The mineral has a wide geographic distribution and is commonly mined as a copper ore.

Locality and naming: The type locality is Freiberg, Saxony, Germany. The name tetrahedrite reflects its crystal forms, with tetrahedral faces frequently observed in well-formed specimens.

Economic and practical significance: Tetrahedrite is an important source of copper and, in some samples, contains minor to appreciable amounts of silver, contributing to its economic value in ore deposits. It is also of interest to mineralogists for its complex solid-solution relationships within the tetrahedrite group.