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Formula: Mn2+7(AsO4)2(OH)8
Anhydrous arsenate containing hydroxyl,
manganese-bearing mineral
Crystal System: Monoclinic
Specific gravity: 3.83 measured, 3.94 calculated
Hardness: 4½
Streak: Greyish to faint brown
Colour: Brown, dark to light purplish red, brownish red, colourless to white
Solubility: Readily soluble in hydrochloric acid
Environments
Metamorphic environments
Hydrothermal environments
Allactite is a rare secondary mineral occurring in low temperature hydrothermal veins associated
with manganese-iron oxide orebodies in dolomitic
marble. At all the locations the basic manganese
arsenates usually occur in close association and have crystallised late with
calcite, pyrochroite
and baryte
(AM 53.733-741).
At Långban, Värmland, Sweden, allactite is associated with
fluorite, synadelphite,
hematolite,
hausmannite,
pyrochroite and
native lead
(Dana).
At the type locality, the Moss mine, Värmland, Sweden, allactite occurs in veinlets through
metamorphosed manganese deposits, associated with fluorite,
synadelphite,
hematolite, hausmannite and
pyrochroite
(Dana, HOM, Mindat).
At Franklin and Sterling Hill, New Jersey, USA, several basic arsenates occur upon cracks in
metamorphosed
franklinite -
willemite - zincite
ore in magnesium-poor marble. Allactite is associated with
pyroaurite, leucophoenicite,
hodgkinsonite, adelite,
franklinite,
willemite, friedelite,
caryopilite,
sphalerite,
fluorite, baryte,
calcite, serpentine
and chlorite
(AM 53.733-741, HOM).
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