Posnjakite Locality: Špania Dolina (Urvölgy; Herrengrund) , Špania Dolina ore belt, Starohorské Mts, Banská Bystrica Region , Slovakia ( Locality at mindat.org ) Field of view 5 mm. Specimen and photo Leon Hupperichs. — Photo: Leon Hupperichs · CC BY-SA 3.0
Posnjakite
A hydrated copper sulfate named for geochemist Eugene Posnjak, described from Kazakhstan in 1967.
Intro adapted from Wikipedia (CC BY-SA).
Posnjakite is an IMA-recognized mineral species in the sulfate class, with the chemical formula Cu₄(SO₄)(OH)₆·H₂O.
It crystallizes in the monoclinic crystal system (space group Pa).
Key properties: Mohs hardness 1.5–3; specific gravity 3.32; Pale blue streak; Vitreous luster; refractive index 1.67; optically biaxial.
IMA symbol Pnk, IMA status: approved, named in 1967.
A secondary mineral formed in the oxidized zone of copper-bearing hydrothermal mineral deposits, commonly of post-mine origin; can occur in slags.
It is found associated with Brochantite, langite, devilline, serpierite, woodwardite, wroewolfeite, aurichalcite, azurite, malachite, chalcopyrite.
The mineral was named to honor Eugene Valdemar Posnjak (1888–1949), Geophysical Laboratory, Washington, D.C., USA, who investigated the CuO−SO3 −H2O system.