Prosopite Locality: Santa Rosa Mine, Noche Buena , Municipio de Mazapil, Zacatecas , Mexico ( Locality at mindat.org ) Unusually bluish prosopite (obtained from Evan Jones). Prosopite can form as an alteration product of Topaz in Topaz-rich greisens; one imagines this is what happened here. This mineral was ID'ed by Evan and folks in Arizona. We have now seen 2 other examples independently labeled the same. (2/15/06) 7.1 x 4.7 x 3.4 cm — Photo: Robert M. Lavinsky · CC BY-SA 3.0
Prosopite
Prosopite is an IMA-recognized mineral species in the halide class, with the chemical formula CaAl₂F₄(OH)₄.
It crystallizes in the monoclinic crystal system (space group C2/c).
Key properties: Mohs hardness 4.5; specific gravity 2.88–2.89; Vitreous, weak luster; optically biaxial.
IMA symbol Psp, grandfathered status — known before the IMA’s founding, named in 1853.
Disseminated in fluorine-rich granites, greisens, and granite pegmatites; more rarely in base-metal deposits.
It is found associated with Fluorite, cryolite, thomsenolite, pachnolite, gearksutite, ralstonite, weberite, jarlite, siderite, hematite, cassiterite, quartz.
Its name comes from the Greek for mask, the mineral’s character being initially masked by pseudomorphism.