Cryptochalcite
Cryptochalcite is an IMA-recognized mineral species in the sulfate class, with the chemical formula K₂Cu₅O(SO₄)₅.
It crystallizes in the triclinic crystal system (space group P-1). It is a member of the Cryptochalcite structural group.
Key properties: Mohs hardness 3; specific gravity 3.411; Pale green streak; Vitreous luster; optically biaxial.
IMA symbol Cpch, IMA status: approved, named in 2015.
Occurs as sublimates on basaltic scoria near a volcanic fumarole (>350-400 flC.).
It is found associated with Cesiodymite, euchlorine, chalcocyanite, dolerophanite, alumoklyuchevskite, anglesite, fedotovite, wulffite, langbeinite, aphthitalite, piypite, klyuchevskite.
Its name comes from the Greek κρυπτόζ, which means “concealed”, and χαλκόζ, which means “copper” in allusion to the natural association concealed among other green copper oxysulfate minerals.