Pharmacolite - Villanière (slag locality), Salsigne, Mas-Cabardès, Carcassonne, Aude, Languedoc-Roussillon, France - View 7.8cm — Photo: Didier Descouens · CC BY 3.0
Pharmacolite
An uncommon hydrated calcium hydrogen arsenate forming soft white fibrous clusters.
Intro adapted from Wikipedia (CC BY-SA).
Pharmacolite is an IMA-recognized mineral species in the arsenate class, with the chemical formula Ca(AsO₃OH)·2H₂O.
It crystallizes in the monoclinic crystal system (space group Ia). It is a member of the Gypsum structural group.
Key properties: Mohs hardness 2–2.5; specific gravity 2.53–2.73; Vitreous, pearly on cleavages luster; refractive index 1.588; optically biaxial.
IMA symbol Pmc, grandfathered status — known before the IMA’s founding, named in 1800.
An uncommon secondary mineral produced through oxidation of earlier arsenic-bearing minerals.
It is found associated with Picropharmacolite, hörnesite, haidingerite.
Its name comes from the Greek for poison, as an arsenic-containing mineral.