Tiemannite Locality: Marysvale District (Marysvale Uranium area), Piute County , Utah , USA ( Locality at mindat.org ) Size: 5 x 5 x 3.9 cm. Tiemannite is a very rare mercury selenide: simply HgSe. This is the classic locality for crystals: tiny black modified tetrahedra. This specimen hosts a few superb, sharp crystals, unusually free of alteration coatings, on matrix. The crystals are small, under 2mm, but very sharp and eye-visible. Another vug, with smaller crystals, lies beneath them. Ex. Philadelphia Academy of Sciences Collection. — Photo: Robert M. Lavinsky · CC BY-SA 3.0
Tiemannite
Mercury selenide — a gray metallic mineral of selenium-rich hydrothermal veins.
Intro adapted from Wikipedia (CC BY-SA).
Tiemannite is an IMA-recognized mineral species in the sulfide class, with the chemical formula HgSe.
It crystallizes in the cubic crystal system (space group F-43m). It is a member of the Sphalerite structural group.
Key properties: Mohs hardness 2.5; specific gravity 8.19–8.47; Nearly black streak; Metallic. R: (400) 34.5, (420) 35.2, (440) 35.0, (460) 34.0, (480) 32.7, (500) 31.6, (520) 30.6, (540) 29.9 luster.
IMA symbol Tmn, grandfathered status — known before the IMA’s founding, named in 1855.
Found in hydrothermal veins with other selenides and calcite.
It is found associated with Clausthalite, eucairite, naumannite, klockmannite, umangite, metacinnabar, galena, sphalerite, barite, manganese oxides, calcite.
The mineral was named to honor Johann Carl Wilhelm Ferdinand Tiemann (1848–1899), chemist of Berlin, Germany, who discovered the mineral.