Stilpnomelane


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Stilp`nom´e`lane


n.1.(Min.) A black or greenish black mineral occurring in foliated flates, also in velvety bronze-colored incrustations. It is a hydrous silicate of iron and alumina.
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The mafic metavolcanic rocks have been metamorphosed to assemblages of actinolite, chlorite, and albitic plagioclase; stilpnomelane has also been reported (Campbell 1990).
In the metagranitoids, the primary plagioclase is typically replaced by albite and epidote-clinozoisite, whereas the primary mafic minerals are replaced by chlorite, amphibole or brown (or more rarely) green stilpnomelane. Highly sheared serpentinites are the most abundant rock type in the ophiolitic melange, they seldom preserve primary igneous minerals but the presence of a chromium-rich spinel is almost pervasive.
Closely associated minerals are: quartz, albite, apatite and stilpnomelane. Other associated minerals are: scandiobabingtonite, scandian ixiolite, hingganite-(Y), cerian epidote, titanite, plumbomicrolite and other microlite minerals, bazzite, milarite cassiterite and two unidentified tantalum minerals (rynersonite?
These include: annabergite, aragonite, argentopentlandite (Sirka, 1988), brochantite, chlorite (group), covellite, devilline, erythrite, gadolinite, gahnite, goethite, gold-silver (electrum), illite, kaolinite, langite, malachite, montmorillonite, natrojarosite, naumannite (Frigstad, 1972), palygorskite, posnjakite, scheelite, sepiolite (van der Wel, 1972), stilpnomelane, sulfur, tetrahedrite and tremolite-actinolite.
The minerals of the matrix are less than 30 microns in size and consist of a rather isotropic intergrowth of K-feldspar, albite, quartz, white mica, chlorite, epidote, allanite, calcite, with accessory stilpnomelane, biotite, pyrrhotite/pyrite, sphalerite, apatite, zircon, and ilmenite decomposed to titanite and rutile.
Stilpnomelane occurs as an accessory mineral in rocks of the district.
Associated minerals are: rhodochrosite, friedelite, hubnerite, sphalerite, stilpnomelane, albite, barite, hausmannite, tephroite, welinite and an unidentified manganese vanadate.