Kosmochlor is a rare chromium sodium clinopyroxene with the chemical formula NaCr3+Si2O6.

Kosmochlor
Chromite (metallic black), kosmochlor pyroxene (emerald green to dark green to black), chromian jadeite pyroxene (green), chromiferous arfvedsonite amphibole (green or gray), symplectite (green, a finely-crystalline mineral mix of mostly chromian jadeite)
General
CategoryInosilicate mineral
Formula
(repeating unit)
NaCr3+Si2O67
IMA symbolKos[1]
Strunz classification9.DA.25
Crystal systemMonoclinic
Crystal classPrismatic (2/m)
(same H-M symbol)
Space groupC2/c
Unit cella = 9.57, b = 8.71
c = 5.26 Å; β = 107.49°; Z = 4
Identification
ColorEmerald-green
Crystal habitPrismatic crystals and fibrous aggregates
TwinningSimple, lamellar on {100} and {001}
CleavageGood on {110} parting on {001}
Mohs scale hardness6
LusterVitreous
StreakLight green
DiaphaneitySemitransparent
Specific gravity3.51-3.60
Optical propertiesBiaxial (-)
Refractive indexnα = 1.766 nγ = 1.781
Birefringenceδ = 0.015
PleochroismX = yellowish green; Y = blue-green, grass-green; Z = emerald-green
Dispersionr > v
References[2][3][4]

The name is from German kosmisch, for its occurrence in meteorites, and the Greek chlor, for green.[4] It was first reported in 1897 from the Toluca meteorite, Jiquipilco, Mexico.[2]

It occurs as a major constituent of some jadeitites and as an accessory mineral of some iron meteorites. Associated minerals include cliftonite (graphite), chromian diopside, troilite at Toluca; daubreelite, krinovite, roedderite, high albite, richterite, chromite (Canyon Diablo); and jadeite, chromite and chlorite (Burma).[3]

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 Kosmochlor on Mindat
  3. ^ a b Kosmochlor in the Handbook of Mineralogy
  4. ^ a b Kosmochlor on Webmin