Eskolaite

Eskolaite
Eskolaite from Russia
General
Category	Oxide mineral
Formula	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).

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 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⁺.

• List of minerals named after people