Johannite Locality: Malwine Shaft, Frohnau , Annaberg-Buchholz , Erzgebirge , Saxony , Germany ( Locality at mindat.org ) Size: thumbnail, 3.5 x 2 x 1.7 cm Johannite This is simply oustanding for the species, among the very best i am told. It is also quite beautiful! Johannite is a very rare uranium mineral — Photo: Robert M. Lavinsky · CC BY-SA 3.0
Johannite
A rare triclinic copper-uranium sulfate forming flaky coatings in oxidized uranium deposits.
Intro adapted from Wikipedia (CC BY-SA).
Johannite is an IMA-recognized mineral species in the sulfate class, with the chemical formula Cu(UO₂)₂(SO₄)₂(OH)₂·8H₂O.
It crystallizes in the triclinic crystal system (space group P-1). It is a member of the Johannite structural group.
Key properties: Mohs hardness 2–2.5; specific gravity 3.32; Pale green streak; Vitreous luster; refractive index 1.594; optically biaxial.
IMA symbol Jh, grandfathered status — known before the IMA’s founding, named in 1830.
A rare secondary mineral found in the oxidized portions of sulfide-bearing uraninite deposits, commonly of post-mine formation.
It is found associated with Gypsum, zippeite, uranopilite, brochantite, chalcanthite.
The mineral was named to honor Austrian Archduke Johann Baptist Josef Fabian Sebastian (1782–1859), founder of the Landesmuseum, Graz, Austria.