Benjaminite
Benjaminite is an IMA-recognized mineral species in the sulfosalt class, with the chemical formula Ag₃Bi₇S₁₂.
It crystallizes in the monoclinic crystal system (space group C2/m). It is a member of the Pavonite structural group.
Key properties: Mohs hardness 3.3–3.5; specific gravity 6.68; Metallic, with greasy appearance. Anisotropism: Strong. R1 –R2: (400) 44.2–47.2, (420) 44.8–47.8, (440) 45.2–48.6 luster.
IMA symbol Bnj, IMA status: approved, named in 1925.
Found in a quartz vein near the contact of a soda-granite and an intrusive rhyolite (Outlaw mine, Nevada); with arsenides (Camsell River, Canada); in a veinlet in calcite (Cobalt, Canada); in a molybdenite pipe deposit (AW mine, Australia).
It is found associated with Aikinite, chalcopyrite, pyrite, covellite, muscovite, molybdenite, quartz (Outlaw mine, Nevada); safflorite, skutterudite, rammelsbergite, arsenopyrite.
The mineral was named to honor Dr. Marcus Benjamin (1857–1932), U.S. National Museum, marine taxonomist and long-time editor of U.S.N.M. publications.