Guérinite , Picropharmacolite Locality: Gabe Gottes Mine (incl. Giftgrube), Ste Marie-aux-Mines (Markirch), Haut-Rhin, Alsace, France White bladed guérinite crystals together with white acicular crystals of picropharmacolite. Field of view 5mm. Specimen and photo Leon Hupperichs. — Photo: Leon Hupperichs · CC BY-SA 3.0
Picropharmacolite
A rare calcium-magnesium arsenate named in 1819 for its bitter magnesium content.
Intro adapted from Wikipedia (CC BY-SA).
Picropharmacolite is an IMA-recognized mineral species in the arsenate class, with the chemical formula Ca₄Mg(AsO₃OH)₂(AsO₄)₂·11H₂O.
It crystallizes in the triclinic crystal system (space group P-1).
Key properties: Mohs hardness 1.5–2; specific gravity 2.62; Feeble pearly to silky luster; refractive index 1.594; optically biaxial.
IMA symbol Ppm, grandfathered status — known before the IMA’s founding, named in 1819.
An oxidation product of arsenic-bearing sulfides in reaction with surrounding calcic rocks; a recent efflorescence in mine workings.
It is found associated with Erythrite, pharmacolite.
Its name comes from the Greek for bitter, in allusion to its magnesium content, and its chemical similarity to pharmacolite.