Jump to content

Groutite

From Wikipedia, the free encyclopedia

This is an old revision of this page, as edited by Addbot (talk | contribs) at 02:01, 8 March 2013 (Bot: Migrating 3 interwiki links, now provided by Wikidata on d:q304018). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

Groutite
Groutite from the Black Water Mine, Black Mesa Basin, Apache County, Arizona, USA
General
CategoryOxide mineral
Formula
(repeating unit)
Mn3+O(OH)
Strunz classification04.FD.10
Crystal systemOrthorhombic
Space groupOrthorhombic dipyramidal
H-M symbol: (2/m 2/m 2/m)
Space group: Pbnm
Unit cella = 4.56 Å, b = 10.7 Å, c = 2.87 Å; Z=4
Identification
ColorJet-black
Crystal habitWedge or lens-shaped crystals; acicular, striated prisms
TwinningReported, unknown law
CleavagePerfect on {010}; less perfect on {100}
FractureUneven
TenacityBrittle
Mohs scale hardness3.5 - 4.0
LusterBrilliant submetallic to adamantine
StreakDark brown
DiaphaneityOpaque
Specific gravity4.144
Optical propertiesBiaxial (+)
Refractive indexnα = 2.100 - 2.200 nγ = 2.100
PleochroismVery strong; X = very dark brown to black; Y = yellowish brown
2V angleMeasured: 40° to 50°
References[1][2][3]

Groutite is a manganese oxide mineral with formula Mn3+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.

Cluster of groutite crystals with kaolinite filling half of a vug in a manganese nodule (size: 3.5 x 3 cm) from the Emilie Mine, Peine, Lower Saxony, Germany

It occurs in weathered banded iron formations, metamorphosed manganese ore bodies and hydrothermal ore environments.[1] 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.[3]

References