Pickeringite Locality: Dubník, Červenica (Czerwenitza), Northern Slanské Mts, Prešov Region, Slovakia Cobalt rich variety of Pickeringite (Kasparite) Field of view 10 mm. Depth of field is achieved with CombineZM. Specimen and photo Leon Hupperichs. — Photo: Leon Hupperichs · CC BY-SA 3.0
Pickeringite
A magnesium-aluminium sulfate forming hair-like efflorescences where pyrite alters in alumina-rich rocks.
Intro adapted from Wikipedia (CC BY-SA).
Pickeringite is an IMA-recognized mineral species in the sulfate class, with the chemical formula MgAl₂(SO₄)₄·22H₂O.
It crystallizes in the monoclinic crystal system (space group P2_1/c). It is a member of the Halotrichite structural group.
Key properties: Mohs hardness 1.5; specific gravity 1.73–1.79; Vitreous luster; refractive index 1.48; optically biaxial.
IMA symbol Pkg, grandfathered status — known before the IMA’s founding, named in 1844.
A common secondary mineral produced through alteration of pyrite in aluminous rocks or in coal seams; in the oxidized zone of pyritic hydrothermal mineral deposits, typically in arid regions, typically post-mining; a fumarolic product.
It is found associated with Kalinite, alunogen, epsomite, melanterite, copiapite, gypsum.
The mineral was named to honor John Pickering (1777–1846), American lawyer and philologist of Boston, Massachusetts, USA.