Simple oxide, hematite group, chromium-bearing mineral
Specific gravity: 5.18
Hardness: 8 to 8½
Solubility: Insoluble in acids or alkalis
Common impurities: V
Eskolaite occurs in chromium-rich
metaquartzite and chlorite
veins. It is a rare component of chondrite meteorites
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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