Piemontite
Piemontite | |
---|---|
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 | |
Colour | 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 |
Lustre | 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 colour, Piemontite has a red streak and a vitreous lustre.[4]
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]
References[]
- ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85: 291–320.
- ^ a b c Handbook of Mineralogy
- ^ Webmineral.com website
- ^ a b c d Mindat reference page for Piemontite
Wikimedia Commons has media related to Piemontite. |
Categories:
- Epidote group
- Calcium minerals
- Aluminium minerals
- Manganese(III) minerals
- Monoclinic minerals
- Minerals in space group 11
- Silicate mineral stubs