Manganhumite

nesosilicate

metamorphic

Formula: Mn2+7(SiO4)3(OH)2
Nesosilicate (insular SiO4 groups), humite group
Specific gravity: 3.83
Hardness: 4
Streak: Yellow-brown
Colour: Pale to deep brownish orange, medium brown
Solubility: Easily soluble in warm diluted hydrochloric acid, leaving a silica gel
Environments:

Metamorphic environments

At Brattforsmine,Sweden, manganhumite is a late-stage skarn mineral formed in recrystallized limestone banded between layers of manganese ore minerals (Webmin), associated with katoptrite, magnetite, manganostibite, magnussonite, tephroite, galaxite and manganosite (Dana, HOM).

At BaldKnob, NorthCarolina, USA, manganhumite occurs in a manganese deposit metamorphosed to the amphibolite facies, associated with sonolite, alleghanyite, rhodonite, kutnohorite, galaxite, jacobsite, kellyite and alabandite (HOM).

Alteration:

manganhumite and H2O to alleghanyite and SiO2
5Mn7(OH)2(SiO4)3 + 2H2O ⇌ 7Mn5(OH)2(SiO4)2 + SiO2
(AM 68.957)

manganhumite and rhodochrosite and H2O to alleghanyite and CO2
2Mn7(OH)2(SiO4)3 + MnCO3 = 3Mn5(OH)2(SiO4)2 + CO2
(AM68.976)

Common impurities: Ti,Al,Fe,Ca,F,H20,P

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