Eskolaite is a rare chromium oxide mineral (chromium(III) oxide Cr2O3).

Eskolaite
Eskolaite from Russia
General
CategoryOxide mineral
Formula
(repeating unit)
Cr2O3
IMA symbolEsk[1]
Strunz classification4.CB.05
Crystal systemTrigonal
Crystal classHexagonal scalenohedral (3 m)
H-M symbol: (3 2/m)
Space groupR3c, No. 167
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 – 8.5
LusterVitreous or metallic
StreakPale green
DiaphaneityOpaque, translucent in thin edges
Specific gravity5.18
DensityMeasured: 5.18 g/cm3, Calculated: 5.20 g/cm3
Optical propertiesUniaxial
PleochroismNoted; emerald-green to olive-green
References[2][3][4]

Discovery and occurrence

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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).

Structure and physical properties

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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+.

See also

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References

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  1. ^ 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.
  2. ^ a b c Eskolaite in the Handbook of Mineralogy
  3. ^ a b Eskolaite on Mindat.org
  4. ^ Eskolaite data on Webmineral.com