Piemontite | |
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![]() Piémontite from the type locality: Prabornaz Mine, Italy | |
General | |
Category | Sorosilicates Epidote |
Formula (repeating unit) | Ca2(Al,Mn3+,Fe3+)3(SiO4)(Si2O7)O(OH) |
IMA symbol | Pmt[1] |
Crystal system | Monoclinic |
Crystal class | Prismatic (2/m) (same H-M symbol) |
Space group | P21/m |
Identification | |
Color | Reddish-brown, reddish-black |
Crystal habit | Slender prismatic, blocky to massive |
Twinning | On [100] uncommon |
Cleavage | [001] good, [100] distinct |
Fracture | Uneven to splintery |
Tenacity | Brittle |
Mohs scale hardness | 6 – 6.5 |
Luster | Vitreous |
Streak | Red |
Diaphaneity | Translucent to nearly opaque |
Density | 3.46 – 3.54 |
Optical properties | Biaxial (+) 2V = 64–106 |
Refractive index | nα = 1.725 – 1.756 nβ = 1.730 – 1.789 nγ = 1.750 – 1.832 |
Birefringence | δ = 0.025 – 0.076 |
Pleochroism | Visible |
Dispersion | r>v very strong |
References | [2][3][4] |
Piemontite is a sorosilicate mineral in the monoclinic crystal system with the chemical formula Ca2(Al,Mn3+,Fe3+)3(SiO4)(Si2O7)O(OH).[2] It is a member of the epidote group.[4]
Red to reddish-brown or red-black in color, piemontite has a red streak and a vitreous lustre.[4] Manganese (Mn3+) causes the red color.[5]
The type locality is the Prabornaz Mine, in Saint-Marcel, Aosta Valley, Italy.[4]
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.[2]
![](http://upload.wikimedia.org/wikipedia/commons/thumb/8/87/Piemontite-Quartz-Calcite-188379.jpg/220px-Piemontite-Quartz-Calcite-188379.jpg)
References
- ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
- ^ a b c Handbook of Mineralogy
- ^ Webmineral.com website
- ^ a b c d Mindat reference page for Piemontite
- ^ "Minerals Colored by Metal Ions". minerals.gps.caltech.edu. Retrieved 2023-03-01.
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