Formula: (K,Ca,Na)(Fe,Mg,Al)8(Si,Al)12(O,OH)36.nH2O phyllosilicate
Specific gravity: 2.59 to 2.96
Hardness: 3 to 4
Streak: White, grey
Colour: Red, brown, black, dark green, dark reddish brown, golden brown
Stilpnomelane can be an important constituent of low-grade, regionally
metamorphosed slate and
and it also occurs in banded iron formations. It
is a mineral of the prehnite-pumpellyite,
In the Kanto mountains, Japan, the minerals associated with stilpnomelane depend on the metamorphic grade.
At low grade metamorphism stilpnomelane is associated with quartz, albite, calcite, graphite and hematite.
At medium grade metamorphism the assemblages are (1) stilpnomelane and chlorite, and (2) lawsonite, stilpnomelane and muscovite variety sericite.
At the highest grade metamorphism the assemblages are (1) muscovite, chlorite and stilpnomelane, (2) chlorite, epidote, garnet and stilpnomelane, (3) chlorite, garnet, muscovite and stilpnomelane.
Common impurities: Ti,Mn,Ca,Na,K,H2O
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