Information AboutGneiss |
| CATEGORIES ABOUT GNEISS | |
| metamorphic rocks | |
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Gneiss is a common and widely distributed type of Rock formed by high grade regional Metamorphic processes from preexisting formations that were originally either Igneous or Sedimentary rocks. Gneissic rocks are coarsely Foliated and largely Recrystallized but do not carry large quantities of Micas , Chlorite or other platy Mineral s. Gneisses that are metamorphosed igneous rocks or their equivalent are termed Granite gneisses, Diorite gneisses, etc. However, depending on their composition, they may also be called Garnet gneiss, Biotite gneiss, Albite gneiss, etc. ''Orthogneiss'' designates a gneiss derived from an igneous rock, and ''paragneiss'' is one from a sedimentary rock. ''Gneissose'' is used to describe rocks with properties similar to gneiss. The word "gneiss" is from an old Saxon mining term that seems to have meant decayed, rotten, or possibly worthless material. The Acasta Gneiss is the oldest known crustal rock in the world. Augen gneiss A coarse grained gneiss, probably originated from metamorphism of igneous granite, whith characteristics eliptic or lenticular feldspaths, normally microcline, contrasting with the ribbon shape of the quartz, biotite and magnetite clusters. Etimology: ''augen'' means eyes in German. SEE ALSO |
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