Gneiss (pronounced /ˈnaɪs/) 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. In Geology, rock is a naturally occurring aggregate of Minerals and/or Mineraloids The Earth's outer solid layer the ‘ Lithosphere Metamorphic rock is the result of the transformation of an existing rock type the protolith, in a process called Metamorphism, which means "change Igneous rocks (etymology from Latin ignis, fire are rocks formed by solidification of cooled Magma (molten rock Sedimentary rock is one of the three main rock types (the others being igneous and Metamorphic rock) Gneissic rocks are usually medium to coarse foliated and largely recrystallized but do not carry large quantities of micas, chlorite or other platy minerals. Foliation is any penetrative planar fabric present in rocks. Foliation is common to rocks affected by regional metamorphic compression typical of orogenic Recrystallization (see also Crystallization) is a physical process that has meanings in Chemistry, Metallurgy and Geology. The word "mica" is thought to be derived from the Latin word la micare, "glitteren" in reference to the brilliant appearance of this mineral (especially The chlorites are a group of phyllosilicate Minerals Chlorites can be described by the following four endmembers based on their chemistry via substitution A mineral is a naturally occurring substance formed through geological processes that has a characteristic chemical composition a highly ordered atomic structure and specific Gneisses that are metamorphosed igneous rocks or their equivalent are termed granite gneisses, diorite gneisses, etc. Granite (ˈɡrænɪt is a common and widely occurring type of intrusive, Felsic, igneous rock. Diorite (ˈdaɪəraɪt is a grey to dark grey intermediate intrusive Igneous rock composed principally of Plagioclase Feldspar (typically However, depending on their composition, they may also be called garnet gneiss, biotite gneiss, albite gneiss, etc. The garnet group includes a group of minerals that have been used since the Bronze Age as gemstones and abrasives Biotite is a common phyllosilicate Mineral within the Mica group with the approximate chemical formula K(Mg Fe3AlSi3O10(F Albite is a plagioclase Feldspar Mineral. It is the sodium endmember of the Plagioclase Solid solution series 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.

Gneiss resembles schist, except that the minerals are arranged into bands. The schists form a group of medium-grade Metamorphic rocks chiefly notable for the preponderance of lamellar Minerals such as Micas chlorite Sometimes it is difficult to tell the difference between gneiss and a schist because some gneiss appears to have more mica than it really does. This is especially true with mica-rich parting planes.

The etymology of the word "gneiss" is disputed. Some sources say it comes from the Middle High German verb gneist (to spark; so called because the rock glitters) and has occurred in English at least since 1757^[1]. Middle High German (MHG German Mittelhochdeutsch) is the term used for the period in the history of the German language between 1050 and 1350 For English usage of verbs see the wiki article English verbs. English is a West Germanic language originating in England and is the First language for most people in the United Kingdom, the United States Other sources claim the root to be an old Saxon mining term that seems to have meant decayed, rotten, or possibly worthless material. The Free State of Saxony (Freistaat Sachsen ˈzaksən Swobodny Stat Sakska is the easternmost federal state of Germany.

See also

• List of rock types

References

Blatt, Harvey and Robert J. This page is intended as a list of all rock types A Amphibolite Andesite Anorthosite Anthracite Tracy, 1996, Petrology: Igneous, Sedimentary and Metamorphic, 2nd ed. , pp. 359-365, Freeman, ISBN 0-7167-2438-3

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