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Formula: Cr2O3
Simple oxide, hematite group,
chromium-bearing mineral
Specific gravity: 5.18
Hardness: 8 to 8½
Streak: Green
Colour: Black
Solubility: Insoluble in acids or alkalis
Common impurities: V
Environments
Metamorphic environments
Hydrothermal environments
Meteorites
Eskolaite occurs in chromium-rich
tremolite skarn,
metaquartzite and chlorite
veins. It is a rare component of chondrite meteorites
(Webmin).
Localities
At the Serra das Almas, Paramirim das Crioulas, Érico Cardoso, Bahia, Brazil, eskolaite occurs as rounded crystals
in stream gravels associated with bahianite and
cassiterite
(Dana).
At the Matoush Uranium deposit, Otish Mountains, Baie-James, Nord-du-Quebec, Quebec, Canada, a
high-chromium mineral assemblage occurs, which is associated with the
Matoush dike intruding sandstone. In addition to
uraninite, chromium-dravite,
chromphyllite and eskolaite are present in major amounts.
Matoush eskolaite contains significant amounts of iron and minimal vanadium substitution
(CM 52.61-75).
At the type locality, the Outokumpu mining district, Outokumpu, North Karelia, Finland, eskolaite
characteristically occurred as hexagonal prisms and plates up to 5 mm in size in
chromium-bearing tremolite
skarn. Although the outokumpu ore is a copper ore, there are in the
orefield about seven million tons of metallic chromium in the
serpentine and skarn rocks.
The specimens most abundant in eskolaite were as follows:
1. In chromium-bearing tremolite
skarn, rich in calcite, from
contact with the ore, eskolaite occurred as hexagonal prisms up to 5 mm in length associated with
pyrrhotite, pentlandite,
chalcopyrite, chromium-bearing
tremolite, uvarovite,
tawmawite, calcite and
talc.
2. In a vein of milky quartz from the foot wall of the ore,
eskolaite occurred as hexagonal prisms up to 1.5 mm associated with
uvarovite, chromium-bearing
tremolite, calcite and
pyrite
3. In veins of pyrrhotite, eskolaite occurred as platy crystals up to
7 mm associated with pyrrhotite,
chromium-bearing tremolite and
chromium tourmaline. In some cases
eskolaite occurs as thin sheets on the surface of quartz.
4. In skarn ore rich in pyrrhotite
eskolaite occurred as short prismatic crystals associated with
chromium-bearing tremolite,
uvarovite, chrome-tourmaline
chromium-rich spinel,
pyrrhotite, pyrite and
chalcopyrite.
5. In chlorite seams eskolaite occurred as thin platy crystals
associated with , pyrite,
chalcopyrite, pyrrhotite
and chromium-rich spinel.
Eskolaite has not been found to occur with chromium-bearing
diopside
(AM 43.1098-1106).
At the Merume river, Kamakusa, Potaro-Siparuni Region, Guyana, eskolaite occurs as pebbles in streams, associated
with guyanaite, bracewellite,
grimaldiite, mcconnellite,
chromium-bearing gahnite,
pyrophyllite and quartz
(HOM, Dana).
At Callowhill Upper, Newton Mt. Kennedy, County Wicklow, Ireland, eskolaite occurs on
graywacke pebbles in a glacial boulder
clay deposit
(HOM).
At the Udachnaya open-pit mine, Daldyn, Mirninsky District, Sakha Republic, Russia, eskolaite has been discovered
intergrown with an octahedral diamond, mostly as an inclusion in the
diamond, but also exposed at its surface.
The eskolaite, containing a picrochromite inclusion, was
formed at high pressure within the diamond stability field
(AM 93.685-690).
At the Clear Creek claim, Goat Mountain, New Idria Mining District, San Benito county, California, USA, eskolaite
occurs as massive green alteration halos around magnesiochromite grains
in the silicified serpentinite rock margins with silica-filled
fractures
(Minrec 36.4.354).
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