{{Short description|Manganese oxide mineral}} {{infobox mineral | name = Groutite | image = Groutite-rare-09-33b.jpg | alt = | caption = Groutite crystals within a manganese nodule | category = Oxide mineral | formula = Mn<sup>3+</sup>O(OH) | IMAsymbol = Gro<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> | molweight = | strunz = 4.FD.10 | dana = | system = Orthorhombic | class = Dipyramidal (mmm) <br/>H-M symbol: (2/m 2/m 2/m) | symmetry = ''Pbnm'' | unit cell = a = 4.56, b = 10.7 <br/>c = 2.87&nbsp;[Å]; Z&nbsp;=&nbsp;4 | color = Jet-black | colour = | habit = Wedge or lens-shaped crystals; acicular, striated prisms | twinning = Reported, unknown law | cleavage = Perfect on {010}; less perfect on {100} | fracture = Uneven | tenacity = Brittle | mohs = 3.5 - 4.0 | luster = Brilliant submetallic to adamantine | streak = Dark brown | diaphaneity = Opaque | gravity = 4.144 | density = | polish = | opticalprop = Biaxial (+) | refractive = n<sub>α</sub> = 2.100 - 2.200 n<sub>γ</sub> = 2.100 | birefringence = | pleochroism = Very strong; X = very dark brown to black; Y = yellowish brown | 2V = Measured: 40° to 50° | dispersion = | extinction = | length fast/slow = | fluorescence = | absorption = | melt = | fusibility = | diagnostic = | solubility = | impurities = | alteration = | other = | prop1 = | references = <ref name=HBM>[http://rruff.geo.arizona.edu/doclib/hom/groutite.pdf Handbook of Mineralogy - Groutite]</ref><ref name=Mindat>[http://www.mindat.org/min-1756.html Groutite on Mindat.org]</ref><ref name=Webmin>[http://www.webmineral.com/data/Groutite.shtml Groutite on Webmineral]</ref> }} '''Groutite''' is a manganese oxide mineral with formula Mn<sup>3+</sup>O(OH). It is a member of the diaspore group and is trimorphous with manganite and feitknechtite. It forms lustrous black crystals in the orthorhombic system.

It occurs in weathered banded iron formations, metamorphosed manganese ore bodies and hydrothermal ore environments.<ref name=HBM/> It was first described in 1945 for an occurrence in the Mahnomen mine, Cuyuna Range, Crow Wing County, Minnesota and named for petrologist Frank Fitch Grout (1880–1958), of the University of Minnesota.<ref name=Webmin/>

==References== {{Reflist}}

Category:Manganese(III) minerals Category:Orthorhombic minerals Category:Minerals in space group 62

{{oxide-mineral-stub}}