polybasite
Polybasite is a gray to black mineral composed of silver, antimony, arsenic, and sulfur. Its chemical formula is generally represented as (Ag,Cu)16Sb2S11. It is a member of the sulfosalt mineral group, characterized by complex structures involving silver, copper, antimony, and sulfur. The ideal end-member formula is Ag16Sb2S11, but it often contains significant amounts of copper, leading to the formula (Ag,Cu)16Sb2S11. Polybasite is typically found in hydrothermal veins, often associated with other silver-bearing minerals. It can also occur in volcanic rocks. Crystals of polybasite are usually short prismatic or tabular. The mineral exhibits a metallic luster and is opaque. Its hardness on the Mohs scale ranges from 2.5 to 3, and its specific gravity is around 6.1 to 6.2. Polybasite is an important ore of silver. Notable occurrences include Mexico, Canada, and various locations in the United States. It is closely related to the mineral pearceite, which has a similar composition but a different crystal structure.
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