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
Environments:
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).
Back to Minerals