Piemontite

Infobox mineral
name = Piemontite
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formula = {Ca₂}{Al₂Mn³⁺} [O|OH|SiO₄|Si₂O₇]
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color = Reddish-brown, reddish-black
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system = Monoclinic
twinning =
cleavage = One perfect, one poor
fracture = Uneven
tenacity = Brittle
mohs = 6
luster = Vitreous
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birefringence = δ = 0.025 - 0.076
dispersion = r>v very strong
pleochroism = Visible
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absorption =
streak = Red
gravity =
density = 3.5
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Piemontite is a sorosilicate mineral in the monoclinic crystal system with the chemical formula {Ca₂}{Al₂Mn³⁺} [O|OH|SiO₄|Si₂O₇] . [http://www.mindat.org/min-3208.html Mindat reference page for Piemontite] ] 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.

It has a brittle fracture, one perfect and one poor cleavage, and a density of 3.5 and a Mohs hardness of 6.

The type locality is the Prabornaz Mine, in Saint-Marcel, Aosta Valley, Italy.

References