Starkeyite
Starkeyite is an IMA-recognized mineral species in the sulfate class, with the chemical formula Mg(SO₄)·4H₂O.
It crystallizes in the monoclinic crystal system (space group P2_1/n). It is a member of the Starkeyite structural group.
Key properties: Mohs hardness 2–3; specific gravity 2.01; Dull luster; optically biaxial.
IMA symbol Ske, IMA status: approved, named in 1945.
An uncommon secondary mineral formed in the presence of iron sulfides; as efflorescences from evaporation of surface and ground waters.
It is found associated with Pyrite, marcasite (Starkey mine, Missouri, USA); konyaite, blödite, gypsum, halite (Great Konya Basin, Turkey); szomolnokite, gunningite (Goldstrike mine.
The name refers to its originally-noted occurrence at the Starkey mine, Missouri, USA.