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Piemontite
Chemical Formula	Ca2(Al,Mn3+,Fe3+)3(SiO4)(Si2O7)O(OH)
Species	Silicates
Crystal System	Monoclinic
Mohs Scale	6
Specific Gravity	3.45
Color	Reddish-brown, reddish-black
Streak	Red
Luster	Vitreous
Refractive Index	n = 1.725 - 1.756 n = 1.730 - 1.789 n = 1.750 - 1.832
Diaphaneity	Translucent, Opaque
Cleavage	PerfectPerfect on Poor on
Fracture	Irregular/Uneven
Crystal Habit：Slender prismatic, blocky to massive
Geological Setting：Greenschist to amphibolite grade regional metamorphism, metasomatised manganese deposits, low temperature hydrothermal veins.

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.