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Apr 23, 2023 · Gneiss is a foliated metamorphic rock that is a common distribute type of rock high-grade regional metamorphic approaches from pre-current formations that have been initially both igneous or sedimentary rocks. It has a glorious banding which is apparent on microscopic scale and hand specimen.
Some specimens of gneiss contain distinctive minerals characteristic of the metamorphic environment. These minerals might include biotite, cordierite, sillimanite, kyanite, staurolite, andalusite, and garnet. Gneiss is sometimes named for these minerals, examples of which include "garnet gneiss" and "biotite gneiss."
Essential minerals - these are minerals that are required within the classification of this rock: Mica > Biotite. K (Fe2+/Mg)2(Al/Fe3+/Mg/Ti) ( [Si/Al/Fe]2Si2O10) (OH/F)2.
Biotite is a name used for a large group of black mica minerals that are commonly found in igneous and metamorphic rocks. These include annite, phlogopite , siderophyllite, fluorophlogopite, fluorannite, eastonite, and many others.
Members of the biotite group are found in a wide variety of igneous and metamorphic rocks. For instance, biotite occurs in the lava of Mount Vesuvius and in the Monzoni intrusive complex of the western Dolomites. Biotite in granite tends to be poorer in magnesium than the biotite found in its volcanic equivalent, rhyolite.
- Massive to platy
- Prismatic (2/m), (same H-M symbol)
- 2.5–3.0
- Monoclinic
In general, gneiss is made from light-colored minerals like quartz and feldspar dark-colored minerals like hornblende, pyroxene, and biotite. Large inclusions of metamorphic minerals like garnet, kyanite, and staurolite and very common.
Jan 8, 2024 · Gneiss can also be classified based on the presence of specific minerals. For example, garnet gneiss contains noticeable amounts of garnet, while biotite gneiss is rich in biotite mica....
