Owyhee County Idaho, USA — Photo: Pacific Museum of Earth from Canada · CC BY-SA 2.0
Naumannite
Silver selenide — an important ore in selenide-rich silver deposits.
Intro adapted from Wikipedia (CC BY-SA).
Naumannite is an IMA-recognized mineral species in the sulfide class, with the chemical formula Ag₂Se.
It crystallizes in the orthorhombic crystal system (space group P2_12_12_1).
Key properties: Mohs hardness 2.5; specific gravity 7–8; Black streak; Metallic. Anisotropism: Distinct but weak, pale gray to dark gray. R1 –R2: (400) 37.2–41.8, (420) 37.0–41.2 luster.
IMA symbol Nau, grandfathered status — known before the IMA’s founding, named in 1828.
Found in hydrothermal veins deficient in sulfur, in association with other selenides, quartz, and carbonates.
It is found associated with Clausthalite, aguilarite, acanthite, tiemannite, umangite, eucairite, argentian tetrahedrite, argentian gold, pyrite, chalcopyrite.
The name refers to German mineralogist and crystallographer Carl Friedrich Naumann (1797–1873).