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Formulae:
jahnsite-(CaFeMg): CaFe2+Mg2Fe3+2(PO4)4(OH)2.8H2O
jahnsite-(CaMnFe): CaMn2+Fe2+2Fe3+2(PO4)4(OH)2.8H2O
jahnsite-(CaMnMg): CaMn2+Mg2Fe3+2(PO4)4(OH)2.8H2O
jahnsite-(CaMnMn): CaMn2+Mn2+2Fe3+2(PO4)4(OH)2.8H2O
Jahnsite-(CaMnZn): CaMn2+Zn2Fe3+2(PO4)sub>4(OH)2.8H2O
Jahnsite-(MnMnFe): Mn2+Mn2+Fe2+2Fe3+2(PO4)4(OH)2.8H2O
jahnsite-(MnMnMg): Mn2+MnMg2Fe3+2(PO4)4(OH)2.8H2O
jahnsite-(MnMnMn): Mn2+Mn2+Mn2+2Fe3+2(PO4)4(OH)2.8H2O
jahnsite-(MnMnZn): Mn2+Mn2+Xn2Fe3+2(PO4)4(OH)2.8H2O
jahnsite-(NaFeMg): NaFe3+Mg2Fe3+2(PO4)4(OH)2.8H2O
jahnsite-(NaMnMg): (Na,Ca)Mn2+(Mg,Fe3+)2Fe3+2(PO4)4(OH)2.8H2O
Hydrated phosphates containing hydroxyl, whiteite group
Data for jahnsite-(CaMnMg)
Specific gravity: 2.706 to 2.718
Hardness: 4
Streak: White
Colour: Brown, golden brown, purplish brown, yellow, yellow orange, greenish yellow
Environments:
Jahnsite occurs as a late-stage hydrothermal decomposition product of primary
triphylite-lithiophilite in complex
granite pegmatites
(HOM). It occurs in a paragenesis with laueite,
strunzite and stewartite (AM 59: 964-973),
associated with
triphylite,
ferrisicklerite-sicklerite series,
heterosite-purpurite series, and
rockbridgeite-frondelite series in vugs
which contain
leucophosphite and huŕeaulite and may be
accompanied by collinsite, hydroxylapatite,
whitlockite, bermanite,
laueite, mitridatite,
segelerite and robertsite
(Dana).
Localities
At Glen Chosaidh, Scotland, UK, jahnsite is associated with graftonite,
johnsomervilleite, mitridatite,
phosphosiderite, rockbridgeite,
vivianite, apatite and
garnet
(HOM).
At the Palermo #1 mine, New Hampshire, USA, jahnsite is associated with laueite and
strunzite
(HOM, AM 59.48-60).
At the type locality, the Tip Top Mine, Custer county, South Dakota, USA, jahnsite is a late stage low-temperature phosphate
mineral in corroded
triphylite-heterosite-ferrisicklerite-rockbridgeite
masses in a granite pegmatite,
associated with
leucophosphite, huŕeaulite,
collinsite, ferrisicklerite,
robertsite, rockbridgeite,
triphylite, tavorite,
messelite and vivianite
(Mindat, HOM, AM 59.48-60).
Localities for other jahnsite minerals
Jahnsite-(CaFeMg)
At the type locality, Tom's Quarry, Mount Lofty Ranges, South Australia, jahnsite-(CaFeMg) occurs as a low-temperature
secondary
phase lining small cavities, and as intergrowths with jahnsite-(NaFeMg) filling veins in a matrix comprising
goethite and minor fluorapatite
(Mindat, AJM 18.1.67).
Jahnsite-(CaMnFe)
At the Fletcher mine, North Groton, New Hampshire, jahnsite-(CaMnFe) occurs with laueite
and strunzite
(Dana).
Jahnsite-(CaMnMn)
At Mangualde, Beira, Portugal, jahnsite-(CaMnMn) is associated with phosphosiderite,
zodacite, varulite and
microcline
(AM 75.401).
Jahnsite-(NaFeMg)
At Tom's Quarry, Mount Lofty Ranges, South Australia, jahnsite-(NaFeMg) is associated with
natrodufrenite, leucophosphite,
kapundaite and mitridatite
(Mindat, AJM 17.1.18).
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