Eskolaite
Eskolaite | |
---|---|
General | |
Category | Oxide mineral |
Formula (repeating unit) | Cr2O3 |
IMA symbol | Esk[1] |
Strunz classification | 4.CB.05 |
Crystal system | Trigonal |
Crystal class | Hexagonal scalenohedral (3 m) H-M symbol: (3 2/m) |
Space group | R3c, No. 167 |
Unit cell | a = 4.95, c = 13.58 [Å]; Z = 6 |
Identification | |
Color | Black to dark green |
Crystal habit | Hexagonal prisms and plates |
Cleavage | None |
Tenacity | Brittle |
Mohs scale hardness | 8 – 8.5 |
Luster | Vitreous or metallic |
Streak | Pale green |
Diaphaneity | Opaque, translucent in thin edges |
Specific gravity | 5.18 |
Density | Measured: 5.18 g/cm3, Calculated: 5.20 g/cm3 |
Optical properties | Uniaxial |
Pleochroism | Noted; emerald-green to olive-green |
References | [2][3][4] |
Eskolaite is a rare chromium oxide mineral (chromium(III) oxide Cr2O3).
Discovery and occurrence
[edit]It was first described in 1958 for an occurrence in the Outokumpu ore deposit of eastern Finland.[3] It occurs in chromium bearing tremolite skarns, metamorphosed quartzites and chlorite bearing veins in Finland; in glacial boulder clays in Ireland and in stream pebbles in the Merume River of Guyana.[2] It has also been recognized as a rare component in chondrite meteorites.[2]
The mineral is named after the Finnish geologist Pentti Eskola (1883–1964).
Structure and physical properties
[edit]Eskolaite crystallizes with trigonal symmetry in the space group R3c and has the lattice parameters a = 4.95 Å and c = 13.58 Å at standard conditions. The unit cell contains six formula units. The lattice is analogous to that of corundum, with Cr3+ replacing Al3+.
See also
[edit]References
[edit]- ^ 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 Eskolaite in the Handbook of Mineralogy
- ^ a b Eskolaite on Mindat.org
- ^ Eskolaite data on Webmineral.com