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	NaCr3+Si2O67
IMA symbol	Kos[1]
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	[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]