Tetrahedrite

Tetrahedrite is a copper antimony sulfosalt, the antimony-rich end member of the tetrahedrite group, forming a solid solution series with the arsenic-dominant tennantite and grading toward the silver-rich variety freibergite. Named for its characteristic tetrahedral crystal habit, it typically forms steel-gray to iron-black, sharply modified triangular crystals, sometimes twinned, and is one of the most widespread sulfosalts on Earth, often carrying significant silver and serving as an important ore of both copper and silver.

Classic historic occurrences include Freiberg in Saxony, the Siegerland district and Rhineland-Palatinate mines in Germany, Příbram in Bohemia, and the mercury-bearing variety schwazite from Schwaz-Brixlegg in Tyrol, Austria. Exceptional collector-grade crystals come from the Herodsfoot Mine in Cornwall, England, typically coated with golden chalcopyrite, while Peru — with the Casapalca, Julcani, and Pasto Bueno deposits — has yielded some of the finest tetrahedrite specimens known. Other notable localities include the Sweet Home Mine in Colorado, the Bingham Canyon Mine in Utah, and the Machacamarca district in Bolivia.

Prized for its lustrous tetrahedral crystal form, occasional iridescent tarnish, and frequent association with chalcopyrite, pyrite, siderite, and calcite, tetrahedrite is a staple of serious sulfide and base-metal collections. Fine, sharp, undamaged crystal clusters — especially from Peru, Cornwall, and the classic German localities — remain highly sought after by systematic and aesthetic collectors alike.