freibergite

Freibergite is a mineral belonging to the tetrahedrite group, with the chemical formula (Ag,Cu)12(Sb,As)4S13. It is a complex sulfosalt mineral characterized by the presence of silver and copper, along with antimony and sometimes arsenic. The ideal composition would be Ag3Cu12Sb4S13, but substitutions are common, leading to a range of compositions. Freibergite is often found as an accessory mineral in hydrothermal ore deposits, particularly those of copper and silver. It typically occurs in association with other copper and silver sulfides, such as chalcopyrite, bornite, and argentite. The mineral commonly forms granular masses or irregular crystalline aggregates, and individual crystals are rare and usually small. Its color is typically iron-black to grayish-black, and it possesses a metallic luster. Freibergite has a Mohs hardness of around 3 to 3.5 and a specific gravity that varies depending on the silver content, generally ranging from 4.5 to 5.2. It is known for its high silver content, making it a potential ore of silver, though it is often too sparsely distributed to be economically mined for this purpose alone. The name freibergite is derived from Freiberg, Germany, a historically significant mining district where the mineral was first described.