Piemontite
Image: <a href="//commons.wikimedia.org/wiki/User:Archaeodontosaurus" title="User:Archaeodontosaurus">Didier Descouens</a> (CC BY 4.0)
Mineral NamePiemontite
Chemical FormulaCa2Al2Mn3+(SiO4)(Si2O7)O(OH)
Mohs Hardness6.5
Crystal Systemmonoclinic
Lustervitreous
Streak Colorreddish-brown to purplish-red
Cleavagegood on {001}, poor on {100}
Fractureuneven to conchoidal
Specific Gravity3.48
Colorsred, reddish-brown, purplish-red
Transparencytranslucent
Type LocalityPrabornaz Mine (ex Praborna Mine), Saint-Marcel, Aosta Valley, Italy
Mineral Groupsilicates
Usescollector, minor ornamental stone
Associated Mineralsquartz, rhodonite, braunite, spessartine, calcite
Rarityuncommon
Description
This specimen features numerous elongated, prismatic crystals of deep reddish-brown to purplish-red piemontite, prominently embedded within a white, granular matrix.
Geological Context
Piemontite is a manganese-rich member of the epidote group, typically forming in metamorphic rocks such as schists and quartzites, often under conditions of low-grade regional metamorphism or hydrothermal alteration.
