This mineral forms tetrahedral-shaped crystals, from which it gets its name. The crystals are often twinned and have a mass of triangular faces. Other habits are granular, massive, and compact. The color is gray to black, and the streak is variable, from black or brown to red. It is opaque and has a metallic luster. Tetrahedrite is grouped chemically with tennantite (below).
FORMATION Forms in hydrothermal veins with sulfides, carbonates, quartz, fluorite, and barite.
TESTS Tetrahedrite is soluble in nitric acid.
Group: SULFOSALTS
Composition: Cu₆Cu₄(Fe,Zn)₂Sb₄S₁₃
Hardness: 3–4½
SG: 4.97
Cleavage: None
Fracture: Uneven to subconchoidal
