Eskolaite

{{Short description|Chromium oxide mineral}} {{infobox mineral | name = Eskolaite | image = Eskolaite.jpg | imagesize = 260px | alt = | caption = Eskolaite from Russia | category = Oxide mineral | formula = Cr₂O₃ | IMAsymbol = Esk<ref>{{Cite journal|last=Warr|first=L.N.|date=2021|title=IMA–CNMNC approved mineral symbols|journal=Mineralogical Magazine|volume=85|issue=3|pages=291–320|doi=10.1180/mgm.2021.43|bibcode=2021MinM...85..291W|s2cid=235729616|doi-access=free}}</ref> | strunz = 4.CB.05 | dana = | system = Trigonal | class = Hexagonal scalenohedral ({{overline|3}} m) <br/>H-M symbol: ({{overline|3}} 2/m) | symmetry = ''R''{{overline|3}}c, No. 167 | unit cell = a = 4.95, c = 13.58&nbsp;[Å]; Z&nbsp;=&nbsp;6 | color = Black to dark green | habit = Hexagonal prisms and plates | twinning = | cleavage = None | fracture = | tenacity = Brittle | mohs = 8 – 8.5 | luster = Vitreous or metallic | streak = Pale green | diaphaneity = Opaque, translucent in thin edges | gravity = 5.18 | density = Measured: 5.18 g/cm³, Calculated: 5.20 g/cm³ | polish = | opticalprop = Uniaxial | refractive = | birefringence = | pleochroism = Noted; emerald-green to olive-green | 2V = | dispersion = | extinction = | length fast/slow = | fluorescence = | absorption = | melt = | fusibility = | diagnostic = | solubility = | impurities = | alteration = | other = | references = <ref name=HBM>[http://rruff.info/doclib/hom/eskolaite.pdf Eskolaite in the Handbook of Mineralogy]</ref><ref name=Mindat>[http://www.mindat.org/min-1411.html Eskolaite on Mindat.org]</ref><ref name=Webmin>[http://www.webmineral.com/data/Eskolaite.shtml Eskolaite data on Webmineral.com]</ref> }} '''Eskolaite''' is a rare chromium oxide mineral (chromium(III) oxide Cr₂O₃).

==Discovery and occurrence== It was first described in 1958 for an occurrence in the Outokumpu ore deposit of eastern Finland.<ref name=Mindat/> 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.<ref name=HBM/> It has also been recognized as a rare component in chondrite meteorites.<ref name=HBM/>

The mineral is named after the Finnish geologist Pentti Eskola (1883–1964).

==Structure and physical properties== thumb|250 px|left|Molar volume vs. pressure at room temperature. Eskolaite crystallizes with trigonal symmetry in the space group ''R''{{overline|3}}''c'' and has the lattice parameters a = 4.95 Å and c = 13.58 Å at standard conditions. The unit cell contains six formula units. The lattice is analogous to that of corundum, with Cr³⁺ replacing Al³⁺. {{clear|left}} ==See also== * List of minerals named after people

==References== {{reflist}}

Category:Chromium minerals Category:Oxide minerals Category:Trigonal minerals Category:Minerals in space group 167 Category:Hematite group Category:Minerals described in 1958

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