| Eskolaite | |
| Category: | Oxide mineral |
| Formula: | Cr2O3 |
| Imasymbol: | Esk[1] |
| Strunz: | 4.CB.05 |
| System: | Trigonal |
| Class: | Hexagonal scalenohedral (m) H-M symbol: (2/m) |
| Symmetry: | Rc, No. 167 |
| Unit Cell: | a = 4.95, c = 13.58 [Å]; Z = 6 |
| Color: | Black to dark green |
| Habit: | Hexagonal prisms and plates |
| Cleavage: | None |
| Tenacity: | Brittle |
| Mohs: | 8 – 8.5 |
| Luster: | Vitreous or metallic |
| Streak: | Pale green |
| Diaphaneity: | Opaque, translucent in thin edges |
| Gravity: | 5.18 |
| Density: | Measured: 5.18 g/cm3, Calculated: 5.20 g/cm3 |
| Opticalprop: | Uniaxial |
| Pleochroism: | Noted; emerald-green to olive-green |
| References: | [2] [3] [4] |
Eskolaite is a rare chromium oxide mineral (chromium(III) oxide Cr2O3).
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).
Eskolaite crystallizes with trigonal symmetry in the space group Rc 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+.