Eskolaite

Eskolaite

Eskolaite from Russia
General
Category Oxide mineral
Hematite group
Corundum structural group
Formula
(repeating unit)
Cr2O3
Strunz classification 4.CB.05
Crystal system Trigonal
Crystal class Hexagonal scalenohedral (3 m)
H-M symbol: (3 2/m)
Space group R3c
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
Luster Vitreous or metallic
Streak Pale green
Diaphaneity Opaque, translucent in thin edges
Specific gravity 5.18
Optical properties Uniaxial
Pleochroism Noted; emerald-green to olive-green
References [1][2][3]

Eskolaite is an uncommon chromium oxide mineral (chromium(III) oxide Cr2O3).

Discovery and occurrence

It was first described in 1958 for an occurrence in the Outokumpu ore deposit of eastern Finland.[2] 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.[1] It has also been recognized as a rare component in chondrite meteorites.[1]

The mineral is named after the Finnish geologist Pentti Eskola (1883–1964).

Structure and physical properties

Molar volume vs. pressure at room temperature.

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+.

References

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