gneiss


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gneiss

(nīs), coarse-grained, imperfectly foliated, or layered, metamorphic rockrock,
aggregation of solid matter composed of one or more of the minerals forming the earth's crust. The scientific study of rocks is called petrology. Rocks are commonly divided, according to their origin, into three major classes—igneous, sedimentary, and metamorphic.
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. Gneiss is characterized by alternating light and dark bands differing in mineral composition and having coarser grains than those of schist. The light bands of gneiss are generally composed of quartzquartz,
one of the commonest of all rock-forming minerals and one of the most important constituents of the earth's crust. Chemically, it is silicon dioxide, SiO2.
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 and feldsparfeldspar
or felspar
, an abundant group of rock-forming minerals which constitute 60% of the earth's crust. Chemically the feldspars are silicates of aluminum, containing sodium, potassium, iron, calcium, or barium or combinations of these elements.
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. Hornblende, biotite mica, garnet, or graphite commonly form the dark bands. Gneisses result from the metamorphism of many igneous or sedimentary rocks, and are the most common types of rocks found in Precambrian regions. Gneiss is found in New England, the Piedmont, the Adirondacks, and the Rocky Mts. Some gneisses are used as facing stone on buildings.

gneiss

A coarse-grained, dark metamorphic rock; composed mainly of quartz, feldspar, mica, and other minerals corresponding in composition to granite, in which the minerals are arranged in layers. See also: Stone

Gneiss

 

a metamorphic rock, foliated, rich in feldspar, and containing smaller quantities of such minerals as quartz, bio-tite, muscovite, amphibole, pyroxene, garnet, and sillimanite.

The formation of gneiss is associated with the deep metamorphism of various rocks and sometimes with fusion because of easily fused granite material in these rocks. As a result of the flow of material, certain granites can acquire the features of gneiss. Gneisses are subdivided into orthogneisses and paragneisses. Orthogneisses are formed from igneous rocks and paragneisses from sedimentary rocks. The foliation of gneiss also varies. In some cases it is a remnant of the initial layering of sedimentary rocks, while in other cases it is a remnant of layered intrusions of igneous material. In addition, foliation may be the result of the viscous flow of fused material during metamorphism. Gneiss is very widely distributed, especially in Precambrian rocks. In folded regions there are gneisses that have been formed by changes in younger rocks under the influence of the pressure developed during the folding process. Gneiss is used to make gravel, pavement slabs, and facing materials.

REFERENCE

Kuznetsov, E. A. Kratkii kurs petrografii (magmaticheskikh i metamorficheskikh porod). Moscow, 1970.

gneiss

[nīs]
(petrology)
A variety of rocks with a banded or coarsely foliated structure formed by regional metamorphism.

gneiss

A coarse-grained metamorphic rock having discontinuous foliation; usually dark; composed mainly of quartz, feldspar, mica, and ferromagnesian minerals. Generally classed as trade granite in the building stone industry.

gneiss

any coarse-grained metamorphic rock that is banded and foliated: represents the last stage in the metamorphism of rocks before melting
References in periodicals archive ?
It represents the fresh and weathered gneiss. The third layer formation appears conducting with very low resistivity ranging from 70.8 to 350 Ohm.m.
The hot spring directly emerges in the Tet fault footwall, in a bloc of gneiss delimited by the three abovementioned faults and surrounded by metasediments.
Salamanca: La Fregeneda, the descent to Muelle de Vegaterron, the Valdaslajas road, banks of the River Agueda, 29TPF7541, 210 m, narrow crevices on highly insolated gneisses, 16.02.2013, Amich, Rico & Sanchez, SALA 146307; ibidem, 29TPF7541, 205 m, narrow fissures on highly insolated gneisses, 07.03.2014, Amich & Ramirez-Rodriguez, SALA 149926.
2003), a long-standing uncertainty has been the relationship between the lower grade units, collectively termed the George River Metamorphlc Suite in the Bras d'Or terrane and the Green Head Group in southern New Brunswick, and the gneissic units, collectively known as the Bras d'Or Gneiss and Brookville Gneiss in the Bras d'Or and Brookville terranes, respectively.
At the confluence of Valsan Valley with Stei Valley we can notice sharp widening of the tributary valley in crystalline schists and gneisses specific for the region with the active slope processes.
The area's geology delineated from geological mapping showed that it consisted of granite, quartzite and varieties of gneiss. Rock type has a direct influence on an area groundwater, as easily fractured rock like quartzite, would enhance secondary porosity and permeability while hard and resistant rock like basalt would adversely affect aquifer parameters.
At Riemvasmaak, some of these are hosted in the pink gneiss, and others in intrusive grey gneiss, granulite, and amphibolite as well as schist (von Backstrom, 1962 and 1967).
The Lithological strata of soils in bore holes drilled in the coastal area is shown in Fig-2 Analysing the Lithological details of bore holes in the study area of Kanyakumari to Colachel, at kanyakumari GL--0.5m is Top Soil, 0.5-9.5m is Leptinite, 9.5-34m is Leptinite Weathered, at Kottaram GL--1.5m is Top soil, 1.54.5m is Gneiss Highly Weathered, 4.5-18m is Gneiss Weathered and at Colachel GL --7m is Top soil, 7-10m is Sand, 10-12m is Clay, 12-17m is Sand stone, 17-19m is Clay.
These include wood from Nova Scotia's Bluenose II schooner, copper from the Library of Parliament roof, a piece of four-billion-year-old Acasta gneiss rock from Great Bear Lake, and more.
Most of the NESP was previously classified as "high-grade gneiss" or "granulite" terrain (i.e.
He also bought 1994 Jersey Stakes winner Gneiss for Julie Cecil, former wife of Henry and another lifelong friend, and he purchased Regal Beauty in America for Jim Joel.