Groutite

minerals

manganite

franklinite

ramsdellite

Images
Formula: Mn3+O(OH)
Oxide, diaspore group, orthorhombic paramorph of trigonal feitknechtite and monoclinic manganite, manganese-bearing mineral
Specific gravity: 4.144
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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