Kosmochlor

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
Category	Inosilicate mineral
Formula (repeating unit)	NaCr3+Si2O67
IMA symbol	Kos
Strunz classification	9.DA.25
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) (same H-M symbol)
Space group	C2/c
Unit cell	a = 9.57, b = 8.71 c = 5.26 Å; β = 107.49°; Z = 4
Identification
Color	Emerald-green
Crystal habit	Prismatic crystals and fibrous aggregates
Twinning	Simple, lamellar on {100} and {001}
Cleavage	Good on {110} parting on {001}
Mohs scale hardness	6
Luster	Vitreous
Streak	Light green
Diaphaneity	Semitransparent
Specific gravity	3.51-3.60
Optical properties	Biaxial (-)
Refractive index	nα = 1.766 nγ = 1.781
Birefringence	δ = 0.015
Pleochroism	X = yellowish green; Y = blue-green, grass-green; Z = emerald-green
Dispersion	r > v
References

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

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).