Eskolaite: Properties and Occurrences

Eskolaite is an uncommon chromium oxide mineral (chromium(III) oxide Cr2O3). It is a somewhat rare chromium oxide in the Hematite group. It is a trigonal-hexagonal scalenohedral mineral containing chromium and oxygen. The mineral is named after the Finnish geologist Pentti Eskola (1883–1964).

It was first described in 1958 for an occurrence in the Outokumpu ore deposit of eastern Finland.

General Information

  • Category: Oxide mineral (Hematite group)
  • Formula: Cr2O3
  • Crystal system: Trigonal
  • Crystal class: Hexagonal scalenohedral (3 m)

Properties

  • Color: Black to dark green
  • Crystal habit: Hexagonal prisms and plates
  • Tenacity: Brittle
  • Mohs scale hardness: 8
  • Luster: Vitreous or metallic
  • Streak: Pale green
  • Diaphaneity: Opaque, translucent in thin edges
  • Specific gravity: 5.18
  • Optical properties: Uniaxial

Occurrence

It occurs in chromium bearing tremolite skarns, metamorphosed quartzites, and chlorite bearing veins in Finland; in glacial boulder clays in Ireland and in stream pebbles in the Merume River of Guyana. It has also been recognized as a rare component in chondrite meteorites.

Association: Guyanaite, pyrrhotite, pentlandite, chalcopyrite, pyrite, chromian tremolite, uvarovite, chromium tourmaline, calcite, talc, quartz (Outokumpu, Finland); guyanaite, bracewellite, grimaldiite, mcconnellite, chromian gahnite, pyrophyllite, quartz (Merume River, Guyana).

 

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