Krausite

Krausite is a yellowish-green mineral composed of hydrous potassium iron sulfate. This specimen is 13 cm across. — Photo: Nessa Eull · CC0

Krausite

Krausite is an IMA-recognized mineral species in the sulfate class, with the chemical formula KFe³⁺(SO₄)₂·H₂O.

It crystallizes in the monoclinic crystal system (space group P2_1/m).

Key properties: Mohs hardness 2.5; specific gravity 2.84; White streak; Vitreous to dull luster; optically biaxial.

IMA symbol Ksi, grandfathered status — known before the IMA’s founding, named in 1931.

Occurs as an uncommon secondary mineral in sulfate-bearing cherts (Borate, California, USA); formed on a dump by post-mine oxidation of pyrite (Velardeña mine, Mexico).

It is found associated with Alunite, coquimbite, römerite, voltaite, metavoltine (Borate, California, USA): copiapite, voltaite, halotrichite (Velardeña mine, Mexico).

The mineral was named to honor Dr. Edward Henry Kraus (1875–1973), American mineralogist, Professor of Mineralogy and Crystallography, University of Michigan, Ann Arbor, Michigan, USA.