Formula: Ca2Mn3+3(SiO4)(Si2O7)(OH)3
Sorosilicate, manganese-bearing mineral
Crystal System: Monoclinic
Specific gravity: 3.43 measured, 3.53 calculated
Hardness: 5
Streak: Brown with reddish tint
Colour: Brown to reddish brown, maroon
Common impurities: Ti,Al,Fe,Cr,V,Cu,Mg,K,Na,H2O

Metamorphic environments
Basaltic cavities

At Manganese lake, Keweenaw county, Michigan, USA, macfallite occurs in basalt associated with manganite, braunite, orientite and pyrolusite. The assemblage replaces calcite in fissures and lenses in the basalt (Dana, HOM, AM 65.406), and most of the crystals are coated with late-stage calcite. Macfallite also occurs with pumpellyite, and these two mineral appear to have formed at the same time (R&M 89.6.508).

At Faggiona, Italy, macfallite replaces braunite under low-temperature metamorphic conditions associated with braunite, quartz and manganoan richterite (HOM).

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