An end-member of the tetrahedrite series from tetrahedrite (Cu,Fe)12Sb4S13 to tennantite (Cu,Fe)12As4S13; if silver is present in quantity (up to 30%) the mineral is called freibergite; sp. gr. 4.5–5.1; hardness 3.0–4.5; greyish-black; metallic lustre; black streak; normally massive but tetrahedral when crystalline; occurs in hydrothermal veins in association with other copper and iron sulphides.