berthierite

Berthierite is a mineral species that is a member of the sulfosalt group. Its chemical formula is FeSb2S4. It is a rare mineral, typically found in hydrothermal veins associated with other antimony and iron minerals. Berthierite is known for its metallic luster and steel-gray to dark gray color. It is an opaque mineral with a relatively low hardness, typically ranking around 2.5 on the Mohs scale. Its specific gravity is approximately 4.2.

The mineral was first described in 1839 and named in honor of the French chemist Pierre Berthier. Berthierite crystallizes in the orthorhombic system, often forming acicular or prismatic crystals, though massive and radiating aggregates are also common. It can also occur as lamellar intergrowths with other minerals.

Geologically, berthierite is found in low to medium temperature hydrothermal environments. It is often associated with minerals such as stibnite, arsenopyrite, pyrite, sphalerite, and quartz. Notable occurrences have been reported in various locations worldwide, including France, Spain, Japan, and the United States. Due to its rarity and relatively soft nature, berthierite has limited economic significance, but it is of interest to mineral collectors and researchers studying sulfosalt mineralogy.