What is "piemontite"

n. (context mineralogy English) A monoclinic sorosilicate mineral of the epidote group, reddish in colour.

Piemontite is a sorosilicate mineral in the monoclinic crystal system with the chemical formula Ca(Al,Mn,Fe)(SiO)(SiO)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.