Formula: Mn2+7(SiO4)3(OH)2
Nesosilicate (insular SiO4 groups), humite group,
manganese-bearing mineral
Crystal System: Orthorhombic
Specific gravity: 3.83 measured, 3.84 calculated
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
Common impurities: Ti,Al,Fe,Ca,F,H20,P
Environments:
Localities
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)
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