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

Eskolaite
Eskolaite.jpg
Eskolaite from Russia
General
CategoryOxide mineral
Hematite group
Corundum structural group
Formula
(repeating unit)
Cr2O3
Strunz classification4.CB.05
Crystal systemTrigonal
Crystal classHexagonal scalenohedral (3 m)
H-M symbol: (3 2/m)
Space groupR3c
Unit cella = 4.95, c = 13.58 [Å]; Z = 6
Identification
ColorBlack to dark green
Crystal habitHexagonal prisms and plates
CleavageNone
TenacityBrittle
Mohs scale hardness8
LusterVitreous or metallic
StreakPale green
DiaphaneityOpaque, translucent in thin edges
Specific gravity5.18
Optical propertiesUniaxial
PleochroismNoted; emerald-green to olive-green
References[1][2][3]

Discovery and occurrenceEdit

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 propertiesEdit

 
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+.

ReferencesEdit