Eskolaite is a rare chromium oxide mineral (chromium(III) oxide Cr2O3).
| Eskolaite | |
|---|---|
 Eskolaite from Russia | |
| 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] |
Discovery and occurrence
editIt 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
editReferences
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