Gneiss

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. Gneissic rocks are usually medium to coarse foliated and largely recrystallized but do not carry large quantities of micas, chlorite or other platy minerals. 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. Image File history File links Gneiss. ... Image File history File links Gneiss. ... This article is about the geological substance. ... Quartzite, a form of metamorphic rock, from the Museum of Geology at University of Tartu collection. ... Igneous rocks (etymology from Latin ignis, fire) are rocks formed by solidification of cooled magma (molten rock), with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. ... Two types of sedimentary rock: limey shale overlain by limestone. ... Foliation is any penetrative planar fabric present in rocks. ... Insulin crystals Recrystallization is an essentially physical process that has meanings in chemistry, metallurgy and geology. ... Rock with mica Mica sheet Mica flakes The mica group of sheet silicate minerals includes several closely related materials having highly perfect basal cleavage. ... Chlorite is a group of phyllosilicate minerals often classified as clays. ... For other uses, see Mineral (disambiguation). ... For other uses, see granite (disambiguation). ... Categories: Mineral stubs | Igneous rocks ... Garnet is a group of minerals that have been used since the Bronze Age as gemstones and abrasives. ... A Biotite slice Biotite is a common phyllosilicate mineral that contains potassium, magnesium, iron and aluminium. ... Albite Albite is an alkali feldspar mineral. ...

Gneiss resembles schist, except that the minerals are arranged into bands. 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. Schist The schists form a group of medium-grade metamorphic rocks, chiefly notable for the preponderance of lamellar minerals such as micas, chlorite, talc, hornblende, graphite, and others. ...

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]. Other sources claim the root to be an old Saxon mining term that seems to have meant decayed, rotten, or possibly worthless material. Middle High German (MHG, German Mittelhochdeutsch) is the term used for the period in the history of the German language between 1050 and 1350. ... It has been suggested that Verbal agreement be merged into this article or section. ... The English language is a West Germanic language that originates in England. ... Location Time zone CET/CEST (UTC+1/+2) Administration Country NUTS Region DED Capital Dresden Minister-President Georg Milbradt (CDU) Governing parties CDU / SPD Votes in Bundesrat 4 (from 69) Basic statistics Area  18,416 km² (7,110 sq mi) Population 4,252,000 (11/2006)[1]  - Density 231 /km...

Augen gneiss

Augen gneiss from Rio de Janeiro, Brazil

Augen gneiss is a coarse-grained gneiss, interpreted as resulting from metamorphism of granite, which contains characteristic elliptic or lenticular shear bound feldspar porphyroclasts, normally microcline, within the layering of the quartz, biotite and magnetite bands. Image File history File linksMetadata Download high resolution version (2254x1801, 719 KB) Augen-gneiss. ... Image File history File linksMetadata Download high resolution version (2254x1801, 719 KB) Augen-gneiss. ... A mylonite showing a number of (rotated) porphyroclasts: a clear red garnet left in the picture while smaller white feldspar porphyroclasts can be found all over. ... Microcline (KAlSi3O8) is an important igneous rock forming tectosilicate mineral. ...

Etymology: from the German Augen (IPA: [ˈaʊgən]), meaning "eyes".

See also

• List of rock types

This page is intended as a list of all rock types. ...

References

Blatt, Harvey and Robert J. Tracy, 1996, Petrology: Igneous, Sedimentary and Metamorphic, 2nd ed., pp. 359-365, Freeman, ISBN 0-7167-2438-3

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