Formula: (K,Ca,Na)(Fe,Mg,Al)8(Si,Al)12(O,OH)36.nH2O
Phyllosilicate (sheet silicate)
Crystal System: Triclinic
Specific gravity: 2.59 to 2.96 measured, 2.667 calculated
Hardness: 3 to 4
Streak: White, grey
Colour: Red, brown, black, dark green, dark reddish brown, golden brown
Common impurities: Ti,Mn,Ca,Na,K,H2O

Metamorphic environments

Stilpnomelane can be an important constituent of low-grade, regionally metamorphosed slate and schist, and it also occurs in banded iron formations. It is a mineral of the prehnite-pumpellyite, greenschist and blueschist facies.

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 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.


The Ma On Shan Mine, Ma On Shan, Sha Tin District, New Territories, Hong Kong, China, is an abandoned iron mine, with both underground and open cast workings. The iron ores contain magnetite as the ore mineral and occur predominantly as masses of all sizes enclosed in a large skarn body formed by contact metasomatism of dolomitic limestone at the margins of a granite intrusion. In parts of the underground workings magnetite is also found in marble in contact with the granite. The skarn rocks consist mainly of tremolite, actinolite, diopside and garnet.
Stilpnomelane is occasionally found as bronze coloured flakes in the skarn, associated with actinolite, diopside, fluorite and magnetite. It replaces actinolite and occurs as infillings of cavities in the skarn (Hong Kong Minerals (1991). Peng, C J. Hong Kong Urban Council)

At Gjerdingselva, Lunner, Viken, Norway, tiny crystals of genthelvite have been observed in miarolitic cavities in the southwestern part of the pluton. At this locality, the mineral content of the cavities includes aegirine (partly decomposed), fluorite, hematite, zircon and stilpnomelane (CM 58.367-379)>

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