16 Oct. 2020 .

"gneiss It is borrowed from the German word Gneis, formerly also spelled Gneiss, which is probably derived from the Middle High German noun gneist "spark" (so called because the rock glitters).[1]. Gneiss nearly always shows a banded texture characterized by alternating darker and lighter colored bands and without a distinct foliation. The rock itself is formed at crustal depths of 10 to 20 km, at pressures of 10kb or more, and temperatures between about 500-700°K, so at depths where rock becomes quasi-viscous, high-grade minerals such as biotite and garnet form that lend a characteristic foliation or banding, but just below temperatures where quartz and feldspar and muscovite begin to melt and/or break down and form veins of granite. layers, or bands, are of different composition.

There is gneiss in Canada that date back 4 billion years. (October 16, 2020).

Sample of gneiss exhibiting "gneissic banding". The Oxford Pocket Dictionary of Current English. This specimen has a composition of an ordinary granite: pink K-feldspar, gray quartz, and black biotite. All gneiss forms as a result of high-grade, regional metamorphic conditions. Gneissic rocks are usually medium- to coarse-foliated; they are largely recrystallized but do no longer deliver large quantities of micas, chlorite or different platy minerals. . Le gneiss ([gnɛs]) est une roche métamorphique de la croûte continentale contenant du quartz, du mica, des feldspaths plagioclases et parfois du feldspath alcalin, tous suffisamment gros pour être identifiés à l'œil nu. to coarse grained; seeing with the naked eye. It is so abundant on the lower level of the Earth’s crust that if you drill anywhere on the surface, you will eventually strike gneiss. Gneiss is medium- to coarse-grained and may contain abundant quartz and feldspar, which some petrographers regard as essential components. Gneiss forms at higher temperatures and pressures than schist. 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. [2], Another cause of banding is "metamorphic differentiation", which separates different materials into different layers through chemical reactions, a process not fully understood.[2]. It has deformed into two sequential forms. The bands that form on gneiss rock are due to the various rocks that are a part of its make-up.

Beautiful floor tiles, facing stone, stair treads, window sills, counter tops, and cemetery monuments are regularly crafted from polished gneiss. [2] These forces stretch out the rock like a plastic, and the original material is spread out into sheets. Gneiss is the principal rock over extensive metamorphic terrains.

Gneiss appears to be striped in bands like parallel lines in shape, called gneissic banding. https://en.wikipedia.org/w/index.php?title=Gneiss&oldid=961169389, Creative Commons Attribution-ShareAlike License. Encyclopedia.com. A gneiss is produced by intense metamorphism, at high temperature and pressure. The Gneiss minerals are order into layer that seeing as Blatt, Harvey and Robert J. Tracy (1996). It forms from volcanic rock, shale, or granitic. Gneissic rocks are usually medium- to coarse-foliated; they are largely recrystallized but do not carry large quantities of micas, chlorite or other platy minerals. Study of gneiss is an important part of metamorphic petrology. The grain size is coarser than that in schists, and layering is often well developed; mineral orientation is less perfect than in schists, however. The second, more warped, form is associated with the Brevard Fault, and the first deformation results from displacement to the southwest. https://en.wikipedia.org/w/index.php?title=Gneiss&oldid=961169389, Short description is different from Wikidata, Articles containing Middle High German (ca. Orthogneiss designates a gneiss derived from an igneous rock, and paragneiss is one from a sedimentary rock. Most of the Outer Hebrides of Scotland have a bedrock formed Gneiss displays distinct foliation, representing alternating layers composed of different minerals. Gneisses that are metamorphosed igneous rocks or their equivalent are termed granite gneisses, diorite gneisses, etc. Orthogneiss is gneiss derived from igneous rock (such as granite). addition to the gneissose texture described above, gneisses tend to be banded [3], Most of the Outer Hebrides of Scotland have a bedrock formed from Lewisian gneiss. band. Gneisses of Archean and Proterozoic age occur in the Baltic In addition to the Outer Hebrides, they form basement deposits on the Scottish mainland west of the Moine Thrust and on the islands of Coll and Tiree. (October 16, 2020). Gneiss forms at higher temperatures and pressures than schist. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates. La foliation, toujours présente, est parfois marquée par l'alternance de petits lits clairs et de fins niveaux plus sombres (on parle alors de litage métamorphique). The word gneiss has been used in English since at least 1757. Gneiss usually does not break up alongside planes of weak point like maximum other metamorphic rocks. word Gneis that mean “spark” (rock glitters). . Along with Gneiss Formation, also learn about Gneiss composition and transformation in the next section. Chemical Composition of Gneiss. The second, more warped, form is associated with the Brevard Biotite, Chlorite, Feldspar, Garnet, Graphite, Hornblade, Micas, Muscovite or Illite, Quartz, Quartzite, Silica, Zircon, Chemical Erosion, Coastal Erosion, Sea Erosion.

The darker bands have A common cause of the banding is the subjection of the protolith (the original rock material that undergoes metamorphism) to extreme shearing force, a sliding force similar to the pushing of the top of a deck of cards in one direction, and the bottom of the deck in the other direction. . alternating lighter and darker sub-parallel discontinuous bands. By signing up for this email, you are agreeing to news, offers, and information from Encyclopaedia Britannica. The mineralogy of a particular gneiss is a result of the complex interaction of original rock composition, pressure and temperature of metamorphism, and the addition or loss of components. Some banding is formed from original rock material (protolith) that is subjected to extreme temperature and pressure and is composed of alternating layers of sandstone (lighter) and shale (darker), which is metamorphosed into bands of quartzite and mica. Schist is also foliated, but it's mineral composition vaires. The darker bands have relatively more mafic minerals (those containing more magnesium and iron). It is formed by the metamorphosis of granite, or sedimentary rock. Gneiss.

Carolina, US, east of the Brevard Shear Zone. Not all gneiss rocks have detectable banding. Gneissic rocks are usually medium- to coarse-foliated; they are largely recrystallized but do no longer deliver large quantities of micas, chlorite or different platy minerals. Gneiss rocks may also be named after a characteristic component such as garnet gneiss, biotite gneiss, albite gneiss, etc. Rocks are naturally occurring solid masses or aggregates of minerals.There are three major types of rocks as sedimentary rocks, igneous rocks, … A common cause of the banding is the subjection of the protolith (the original rock material that undergoes metamorphism) to extreme shearing force, a sliding force similar to the pushing of the top of a deck of cards in one direction, and the bottom of the deck in the other direction. of Coll and Tiree. Granitic gneiss has a mineral composition similar to that of granite. Some also contain larger crystals imbedded in the rock matrix, most frequently garnet, topaz, and beryl minerals. sequential forms. Henderson gneiss is found in North Carolina and South Carolina, US, east of the Brevard Shear Zone. Updates? Gneisses that are metamorphosed igneous rocks or their equivalent are termed granite gneisses, diorite gneisses, etc.

It rocks that originate as sedimentary rock are called paragneiss and those originating as igneous rock are called orthogneiss. Gneiss formation took place millions of years ago. [2] The banding is developed under high temperature and pressure conditions. Schist is a metamorphic rock usually formed originally from shale. The grain size is coarser than that in schists, and layering... Get exclusive access to content from our 1768 First Edition with your subscription. A highly foliated, coarse-grained metamorphic rock consisting of light-colored layers, usually of quartz and feldspar, alternating with dark-colored layers of other minerals, usually hornblende and biotite.

This article was most recently revised and updated by, https://www.britannica.com/science/gneiss. Augen gneiss, from the German: Augen [ˈaʊɡən], meaning "eyes", is a coarse-grained gneiss 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. It has a glorious banding which is apparent on microscopic scale and hand specimen. It has deformed into two sequential forms. Henderson gneiss is found in North Carolina and South Carolina, US, east of the Brevard Shear Zone. The minerals are arranged into layers that appear as bands in cross section. it has been subjected to higher temperatures and pressures than schist. [2] The appearance of layers, called 'compositional banding', occurs because the layers, or bands, are of different composition. For the casual student, it is convenient to think of a gneiss as a rock with parallel, somewhat irregular banding which has little tendency to split along planes. T. F. HOAD "gneiss Gneiss can be classified on the basis of minerals that are present, presumed formational processes, chemical composition, or probable parent material. This page was last edited on 7 June 2020, at 00:13.