Tetraeedrite

Tetrahedrite is a copper antimony sulfide mineral with the formula Cu12Sb4S13. It is the main endmember of the tetrahedrite group, a family of complex sulfosalts that commonly occurs in hydrothermal ore veins. It typically forms metallic, gray to black crystals and occurs in association with quartz, calcite, galena, sphalerite, and other sulfides.

Chemically, tetrahedrite forms a solid solution with the arsenic analogue tennantite (Cu12As4S13). In natural samples, copper can be partially replaced by iron and zinc, and silver can substitute for copper to yield argentotetrahedrite. These substitutions produce a range of compositions within the tetrahedrite-tennantite series.

Crystallography and appearance: Tetrahedrite crystals are often small but may form well-shaped euhedra in the cubic system. The mineral has a metallic luster and a dark gray to black color. On the Mohs scale, its hardness is about 3.5 to 4, and it has a relatively high density, typically around 4.5 to 5.0 g/cm3.

Occurrence and significance: It occurs worldwide in hydrothermal veins and skarn deposits. Tetrahedrite is an ore mineral of copper in many deposits and can be accompanied by byproducts such as arsenic and antimony. Its economic importance varies with the grade and accessibility of the deposit.

Name and distribution: The name derives from its tetrahedral crystal forms observed in some specimens. Tetrahedrite has been known since the 18th–19th centuries and remains widely distributed, with notable localities in Europe and the Americas.