Allactite

arsenate

manganese minerals

Formula: Mn2+7(AsO4)2(OH)8
Anhydrous arsenate containing hydroxyl
Specific gravity: 3.83
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

Hydrothermal environments

Allactite is a rare secondary mineral restricted to low temperature hydrothermal vein systems 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 Langban, 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, associated with pyroaurite, leucophoenicite, hodgkinsonite, adelite, franklinite, willemite, friedelite, caryopilite, sphalerite, fluorite, baryte, calcite, serpentine and chlorite (AM53.733-741, HOM).

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