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Formula: NaCr3+Si2O6
Inosilicate (chain silicate), clinopyroxene subgroup,
pyroxene group,
chromium-bearing mineral, forms a series with
jadeite
Crystal System: Monoclinic
Specific gravity: 3.51 to 3.60 measured, 3.60 calculated
Hardness: 6
Streak: Pale green
Colour: Emerald-green
Common impurities: Ti,Al,Fe,Mn,Mg,Ca,K,P
Environments
Metamorphic environments
Meteorites
Kosmochlor is a major constituent of some jadeitites and an
accessory constituent of some iron meteorites
(HOM).
Localities
At the Coahuila meteorite, Ocampo Municipality, Coahuila, Mexico, kosmochlor is associated with
daubréelite
(HOM).
At the type locality, the Toluca meteorite, Jiquipilco, Mexico, koskochlor is found as a residue after
dissolution of the iron meterorite, associated with
graphite and troilite
(Mindat).
At Tawmaw, Hpakant-Tawmaw Jade Tract, Hpakant Township, Mohnyin District, Kachin State, Myanmar, four distinct
textures and related compositions of kosmochlor and
chromium-bearing jadeite occur in
rocks from the Myanmar jadeitite area:
(1) spheroidal or ellipsoidal aggregates with a corona texture surrounding relict
chromite
(2) spheroidal or ellipsoidal aggregates with a core of jadeite
(3) granoblastic textures in undeformed coarse-grained clinopyroxene
rocks
(4) recrystallised fine-grained aggregates in deformed jadeitite
Nearly pure kosmochlor was found in type 2 textures, closest to the end-member reported so far from a
terrestrial rock.
The preservation of relict chromite in the centre of coronitic spheroidal
or ellipsoidal aggregates of kosmochlor and jadeite indicates a
metasomatic origin from a peridotite protolith at an inferred
minimum pressure of 1.0 GPa and temperatures of 250 to 370°C
(MM 69.1059-1075).
Kosmochlor from Tawmaw - Image
At the Canyon Diablo meteorite, Meteor Crater area, Coconino County, Arizona, USA, kosmochlor is associated
with krinovite, roedderite,
high albite, richterite and
chromite
(HOM).
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