Jahnsite

triphylite

laueite

Formula:
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-(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:

Pegmatites

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, huŕeaulite and may be accompanied by collinsite, hydroxylapatite, whitlockite, bermanite, laueite, mitridatite, segelerite and robertsite (Dana).

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).

Back to Minerals