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Formula: CaMn2+Fe2+2Fe3+2(PO4)4(OH)2.8H2O
Hydrated phosphate containing hydroxyl,
jahnsite subgroup,
jahnsite group,
manganese-bearing
mineral
Crystal System: Monoclinic
Specific gravity: 2.86 measured, 2.88 calculated
Hardness: 4
Streak: White
Colour: Brown, golden brown, purplish brown, yellow, yellow-orange
Luminescence: Not fluorescent under UV
Environments
Pegmatites
Hydrothermal environments
Jahnsite-(CaMnFe) is a late-stage hydrothermal decomposition product of
primary phosphate minerals in complex
granite pegmatites
(HOM).
Localities
At the Sapucaia mine, Sapucaia do Norte, Galiléia, Minas Gerais, Brazil, jahnsite-(CaMnFe) is associated with
frondelite, bermanite,
hureaulite, strunzite and
johnsomervilleite
(HOM).
At the Hagendorf South Pegmatite, Hagendorf, Waidhaus, Neustadt an der Waldnaab District, Upper Palatinate, Bavaria, Germany,
secondary phosphate assemblages containing the new (in 2010)
manganese-aluminium phosphate mineral,
nordgauite, have been studied.
Nordgauite nodules enclose crystals of the
jahnsite–whiteite group of minerals,
showing pronounced compositional zoning, spanning the full range of Fe/Al ratios between
jahnsite and whiteite. The
whiteite-rich members are fluorine-bearing, whereas the
jahnsite-rich members contain no fluorine. Associated minerals include
sphalerite, apatite,
parascholzite,
zwieselite-triplite solid solutions
and a kingsmountite-related mineral. The average compositions of
whiteite and jahnsite from different
zoned regions correspond to jahnsite-(CaMnMn),
whiteite-(CaMnMn) and
whiteite-(CaMnFe) end-members
(MM 74.969-978).
At the type locality, the Fletcher mine, Groton, Grafton county, New Hampshire, USA, jahnsite-(CaMnFe) occurs as
clusters of brown striated tablets associated with rockbridgeite in a late
stage phosphate mineralisation in a granite
pegmatite
(Mindat, HOM).
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