Phaunouxite Locality: Gabe Gottes Mine (incl. Giftgrube), Ste Marie-aux-Mines (Markirch), Haut-Rhin, Alsace, France Clusters of tiny phaunouxite crystals together with some acicular picropharmacolite crystals. Field of view 4mm. Specimen and photo Leon Hupperichs. — Photo: Leon Hupperichs · CC BY-SA 3.0
Phaunouxite
Phaunouxite is an IMA-recognized mineral species in the arsenate class, with the chemical formula Ca₃(AsO₄)₂·11H₂O.
It crystallizes in the triclinic crystal system (space group P-1).
Key properties: specific gravity 2.28; Vitreous luster; optically biaxial.
IMA symbol Pnx, IMA status: approved, named in 1980.
A very rare post-mine low-temperature reaction product of carbonate gangue with arsenical solutions derived from arsenic (Sainte-Marie-aux-Mines, France).
It is found associated with Picropharmacolite, pharmacolite, sainfeldite, rauenthalite, ferrarisite, löllingite, calcite, aragonite (Sainte-Marie-aux-Mines, France).
The name comes from Phaunoux, the French name for the Rauenthal Valley, France, within which the mineral was first found.