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Formula: Mn3+O(OH)
Hydroxide, diaspore group, orthorhombic
paramorph of trigonal
feitknechtite and monoclinic
manganite, manganese-bearing
mineral
Crystal System: Orthorhombic
Specific gravity: 4.144 measured, 4.172 calculated
Hardness: 3½ to 4
Streak: Dark brown
Colour: Black, may be iridescent
Environments:
Sedimentary environments
Hydrothermal environments
Groutite is a secondary mineral lining vugs in weathered
banded ironstone formations (Webmin). Associated minerals
include manganite, hematite,
goethite, lepidocrocite,
quartz and calcite
(HOM).
Localities
At the Walton baryte mine, Walton, Hants county, Nova Scotia, Canada, groutite has been found. The principal
hypogene minerals here are
baryte, siderite,
pyrite, marcasite,
galena, sphalerite,
tennantite, proustite,
chalcopyrite and acanthite.
Less common are quartz, pyrite variety
bravoite,
stromeyerite, pearceite,
gersdorffite, clausthalite
and penroseite. The main
supergene minerals include
limonite, goethite,
pyrolusite, malachite,
azurite, erythrite,
lavendulan, moorhouseite,
aplowite, chalcanthite,
szomolnokite, metavoltine and
chalcocite. Of less certain origin are
hematite, kaolinite,
calcite and covellite
(CM 9.718-720).
At Ilfeld, Harztor, Nordhausen District, Thuringia, Germany, Ilfeld, Hartz mountains, crystals of groutite
to 2 have been found cm with manganite
(Min Rec 41-6).
At the Magma mine, Pioneer District, Pinal county, Arizona, USA, groutite has been found with a few blebs of
rhodochrosite in the hydrothermal ore body
(R&M 95.1.85, HOM).
There are two co-type Localities, the Mahnomen pit, and the Sagamore Mangan No. 2 pit, both at Ironton, Cuyuna North
Range, Crow Wing county, Minnesota, USA.
The groutite crystals occur as a late stage secondary
mineral, and always line vugs in the banded ironstone formation, and
nearly always are associated with manganite. The only other associated
minerals are quartz, hematite and
goethite. A thin coating of calcite
may be found on some specimens
(AM 32.654-659, HOM).
At Franklin, Franklin Mining District, Sussex County, New Jersey, USA, an
antimony-bearing groutite occurs in
franklinite and andradite in
the metamorphosed stratiform zinc orebody
(AM 52.858).
At Talcville, St. Lawrence county, New York, USA, groutite occurs with
calcite in vugs in manganiferous
talc schist (HOM, Dana).
This occurrence suggests that the calcite provided the alkaline environment
which is necessary for the formation of the groutite.
It seems logical that acid waters dissolved some of the Mn from the host rocks and that these solutions were neutralised
by contact with the calcite, creating the conditions for the formation of
groutite
(AM 44.877-878).
Alteration
groutite and oxygen to ramsdellite
At the Gavilan mine, Los Gavilanes, Mun. de Tecate, Baja California, Mexico,
ramsdellite pseudomorphs
after groutite are formed by the oxidation reaction
groutite and oxygen to ramsdellite
4MnO(OH) + O2 → 4MnO2+2.H2O
(AM 47.47-58)
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