Category SorosilicatesEpidote Space group P21/m | Crystal system Monoclinic | |
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Formula(repeating unit) Ca2(Al,Mn,Fe)3(SiO4)(Si2O7)O(OH) Crystal class Prismatic (2/m)(same H-M symbol) Colour Reddish-brown, reddish-black | ||
Piemontite is a sorosilicate mineral in the monoclinic crystal system with the chemical formula Ca2(Al,Mn3+,Fe3+)3(SiO4)(Si2O7)O(OH). It is a member of the epidote group.
Red to reddish-brown or red-black in colour, Piemontite has a red streak and a vitreous lustre.
The type locality is the Prabornaz Mine, in Saint-Marcel, Aosta Valley, Italy.
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.
References
Piemontite Wikipedia(Text) CC BY-SA