Piemontite is a sorosilicate mineral in the monoclinic crystal system with the chemical formula Ca2(Al,Mn3+,Fe3+)3(SiO4)(Si2O7)O(OH).[1] It is a member of the epidote group.[3]
Red to reddish-brown or red-black in colour, Piemontite has a red streak and a vitreous lustre.[3]
The type locality is the Prabornaz Mine, in Saint-Marcel, Aosta Valley, Italy.[3]
It occurs metamorphic rocks of the greenschist to amphibolite metamorphic facies and in low-temperature hydrothermal veins in altered volcanic rocks. It also occurs in metasomatized deposits of manganese ore. Associated minerals include: epidote, tremolite, glaucophane, orthoclase, quartz and calcite.[1]
References
Handbook of Mineralogy
Webmineral.com website
Mindat reference page for Piemontite
