Freibergite
specimen number:
2273024
location:
Sunshine Mine, Shoshone Co., Idaho, USA
description: The Sunshine Mine, located in the Coeur d'Alene mining district of Shoshone County, Idaho, is historically one of the most prolific and deepest underground silver operations in the United States. Geologically, the deposit consists of complex polymetallic hydrothermal veins hosted within folded and faulted Neoproterozoic quartzites and argillites of the Belt Supergroup, specifically the Wallace, St. Regis, and Revett formations. The primary ore mineralization features silver-bearing tetrahedrite embedded within a gangue of siderite and quartz, alongside localized sulfides like chalcopyrite, galena, and pyrite. Discovered in 1884 by the Blake brothers, the property saw sporadic early work before formal underground production expanded significantly around 1890. Under the long-term stewardship of the Sunshine Mining Company, organized in 1918, the mine became a dominant industrial force, maintaining near-continuous silver extraction through the twentieth century despite a catastrophic underground fire in 1972. Depleted high-grade reserves and shifting economic realities ultimately led to the cessation of commercial mining operations in 2001, leaving a legacy of over 360 million ounces of produced silver. Freibergite is a complex sulfosalt mineral and the silver-dominant member of the tetrahedrite group that crystallizes in the cubic system. Geologically, it develops as a primary mineral within low-to-medium temperature hydrothermal vein deposits, typically forming in structural zones alongside other base metal sulfides and silver sulfosalts like galena, sphalerite, chalcopyrite, and polybasite. Chemically intermediate, it forms continuous solid-solution series with both tetrahedrite and argentotennantite, where significant portions of copper and arsenic substitute into the crystal lattice alongside essential silver, antimony, iron, and sulfur. The mineral characteristically occurs as steel-gray to iron-black tetrahedral crystals or massive granular aggregates that exhibit an opaque diaphaneity, uneven fracture, and a brilliant metallic luster on fresh surfaces. Because of its exceptionally high silver content, freibergite serves as a critical economic component of major silver ore bodies worldwide, frequently determining the viability of extraction projects within complex mineralized systems.
Metallic lustrous crystals of freibergite on a siderite crystal matrix. In good condition.
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