Berthierite. Pen for scale.No locality given. Mineral collection of Bringham Young University Department of Geology, Provo, Utah. Photograph by Andrew Silver. BYU index 3-4010, FeS - Sb_2S_3. — Photo: Wikimedia Commons · Public domain
Berthierite
A steel-gray iron-antimony sulfide often mistaken for stibnite; iridescent tarnish is common.
Intro adapted from Wikipedia (CC BY-SA).
Berthierite is an IMA-recognized mineral species in the sulfosalt class, with the chemical formula FeSb₂S₄.
It crystallizes in the orthorhombic crystal system (space group Pnma). It is a member of the Berthierite structural group.
Key properties: Mohs hardness 2–3; specific gravity 4.64; Dark brownish gray streak; Metallic luster.
IMA symbol Btr, grandfathered status — known before the IMA’s founding, named in 1827.
Found in low-temperature hydrothermal antimony veins, in portions deficient in sulfur.
It is found associated with Stibnite, arsenopyrite, pyrite, barite, calcite, quartz.
The name refers to Pierre Berthier (1782–1861), French chemist.