Gneiss is characterized by alternating light and dark bands differing in mineral composition and having coarser grains than those of schist. The origin of a gneiss can usually be determined by its chemical composition and mineral content. The term gneiss was brought to scientific usage from the german language. Therefore, the best you can do is to report the chemical composition of the minerals found in the gneiss. Gneiss is a common and widely distributed type of metamorphic rock.
Pages in category gneiss the following 10 pages are in this category, out of 10 total. Orthogneiss designates a gneiss derived from an igneous rock, and paragneiss is one from a sedimentary rock. They form the basement on which the torridonian and moine supergroup sediments were deposited. Gneiss is formed by high temperature and highpressure metamorphic processes acting on formations composed of igneous or sedimentary rocks. Most gneiss has very a similar composition to granite. Enter your mobile number or email address below and well send you a link to download the free kindle app. Because gneiss are a type of metamorphic rock with uneven granular medium to coarse grained crystalline with varied degree of mineral bearings, its general application in buildings, construction and civil engineering works is unique. Turn left for rocks deformed and heated again in the later laxfordian episode. Minerals have specific chemical comppositions, that is, minerals are compounds, but rocks are mixtures of two or more minerals and have variable compositions. Gneiss is a spreadsheet tool for using and analyzing online data. Includes protomylonite, mylonite, ultramylonite, and cataclastic rocks. A banded or foliated metamorphic rock, usually of the same composition as granite. No recent coverage index constantly checks hot and trending companies for their latest activity.
It is characterized by alternating light and dark bands differing in mineral composition. Contains a wide variety of rock types including graphitic schist and marble. Lewisian gneiss synonyms, lewisian gneiss pronunciation, lewisian gneiss translation, english dictionary definition of lewisian gneiss. Shop for composition notebooks in office products on.
In most mapped belts of mylonite and cataclastic rock my, tectonized rocks anastomose around lenses of lessdeformed or undeformed rock. Jul 14, 2014 the only catch is that gneiss is a rock and rocks are mixtures of minerals. The lighter bands contain mostly quartz and feldspar, the darker often contain biotite, hornblende, garnet or graphite. Lewisian gneiss western isles rocks and geology photos. Lewisian gneiss, one of the oldest rocks in great britain, three billion years old, two thirds the age of the earth read about the geology of the outer hebrides the isle of lewis and the isle of harris rocks and the callanish stones.
As further reading, i recommend the excellent book by ron h. The light bands of gneiss are generally composed of quartz quartz, one of the commonest of all rockforming minerals and one of the most important constituents of the earths crust. Orthogneiss is gneiss derived from igneous rock such as granite. High grade metamorphic rocks of the scourian episode. In quebec, gneiss production for architectural uses has been reported in 35 areas. Lewisian gneiss rock of the outer hebrides western isles. Gneiss have always served mankind in road construction and general building works. The layering of a gneiss may be weak or welldeveloped and consists of varying concentrations of biotite, garnet, hornblende, mica, and other minerals. Geochemical data from the 625 ma massabesic gneiss complex of southern new hampshire show strong af. It is a blazon of metamorphic bedrock that is formed during extreme exposure of igneous or sedimentary rocks to acute pressure and temperature. Although a gneiss is commonly feldspar and quartzrich, the mineral composition is not an essential factor in its definition. Gneiss definition in the cambridge english dictionary. Lithology highly variable, depending on the nature of the parent rock, and on intensive parameters and history of deformation.
The dominant rock type is grayish gneiss that is rich in quartz, feldspar, and ironrich minerals. Turn right for the oldest highgrade metamorphic rocks. Paragneiss is gneiss derived from sedimentary rock such as sandstone. Lewisian gneiss definition of lewisian gneiss by the free. Paragneiss is gneiss derived from sedimentary rock. Gneissose is used to describe rocks with properties similar to gneiss. A wide range of minerals are important as accessories and are characteristic either of the protolith. For geological data and further information, click on the name of the area you are interested in. Gneiss displays distinct foliation, representing alternating layers composed of different minerals. The lewisian complex or lewisian gneiss is a suite of precambrian metamorphic rocks that outcrop in the northwestern part of scotland, forming part of the hebridean terrane and the north atlantic craton. It is characterized by alternating light and dark bands differing in mineral composition coarser grained than schist. Gneiss forming from sedimentary rock is called paragneiss and can form from shale, sandstone or basalt while gneiss forming from igneous rock is called orthogneiss and typically forms from granite, gabbro, or diorite. It is this banded appearance and texture rather than composition that define a gneiss. Knot gneiss by piers anthony, 2010, tor edition, in english.
The lewisian, torridonian and moine of scotland are basement lewisian and cover rocks formed on the eastern margin of laurentia between about 3000 ma and 900 ma i. Other bands contain platy or elongate minerals with evidence of preferred orientation. In the region where they occur, lewisian rocks form the basement, or lowermost, rocks. Gneiss pronounced nice is a metamorphic rock consisting mostly of quartz and feldspar and showing distinct layering or banding.
Mylonite, mylonite gneiss, and cataclastic rocks vamy. Get unlimited access to the best stories on medium and. Gneiss granofels and migmatite gneiss and granofels range in composition from felsic to intermediate to mafic. Lewisian gneiss article about lewisian gneiss by the free. How can a schist can be transformed to augengneiss. These rocks are of archaean and paleoproterozoic age, ranging from 3. Composition and texture of gneiss although gneiss is not defined by its composition, most specimens have bands of feldspar and quartz grains in an interlocking texture. Western isles rocks lewisian gneiss geology isle of lewis isle of harris the geology of the outer hebrides is really important as the predominant rock type is a lewisian gneiss a metamorphic rock which is astonishingly up to 3 billion years old, making it the oldest rock in britain two thirds the age of the earth. Gneiss is a type of foliated metamorphic rock that is very. Free next day delivery on eligible orders for amazon prime members buy composition books on.
Lewisian gneiss rock of the outer hebrides western. It is formed by the metamorphosis of granite, or sedimentary rock. They are classified below in alphabetical order, rather than according to the volume of rock extracted. The minerals are arranged into layers that appear as bands in cross section. Gneiss definition of gneiss by the free dictionary. Gneiss gneiss is a high grade metamorphic rock, meaning that it has been subjected to higher temperatures and pressures than schist. Isle of lewis geology the rocks of lewis and the isle of harris the geology of the outer hebrides is really important as the predominant rock type is a lewisian gneiss a metamorphic rock which is astonishingly up to 3 billion years old, making it the oldest rock in britain two thirds the age of the earth. These bands are usually light in color and alternate with bands of darkercolored minerals with platy or elongate habits. Files are available under licenses specified on their description page. Gneiss is a foliated metamorphic rock identified by its bands and lenses of varying composition, while other bands contain granular minerals with an interlocking texture.
Gneiss is a medium to coarsegrained, semischistose metamorphic rock. It is this banded appearance and texture rather than composition that. Then you can start reading kindle books on your smartphone, tablet, or computer no kindle device required. Affordable and search from millions of royalty free images, photos and vectors. Gneiss from evje, norway, containing more feldspar and quartz than lewisian gneiss from scotland, giving it a pink colour, these specimens show excellent banding and text book crystal structure, supplied in 3 sizes, ideal for educational use. The geochemistry of lewisian amphibolitefacies gneisses from northwest scotland is described with particular reference to the rare earth elements ree and compared with the geochemistry of lewisian granulitefacies gneisses.
Lewisian gneiss geochemistry and archaean crustal development models. Pdf the hallandia gneiss, a swedish heritage stone resource. Muscovite gneiss, biotite gneiss and muscovitebiotite gneiss, more common perhaps than all the others taken together, are grey or pinkish rocks according to the colour of their prevalent felspar, not unlike granites, but on the whole more often finegrained though coarsegrained types occur and possessing a gneissose or foliated structure. The common mineral components are quartz, feldspar, micas, and silicates. During regional metamorphism a granitic augen gneiss can be transformed. Lewisian complex, major division of precambrian rocks in northwestern scotland the precambrian began about 4.
Gneiss is a metamorphic rock form characterized by banding caused by segregation of different types of rock, typically light and dark silicates. Choose from 10 different sets of gneiss flashcards on quizlet. The hallandia gneiss, a swedish heritage stone resource article pdf available in geological society london special publications 4071. A distinction between gneiss and schist is difficult to draw, for many gneisses look far richer in mica than they are, when mica rich parting plane is seen. Lewisian rocks originally consisted of both igneous and sedimentary rocks that have been altered from their original composition and structure through time by heat, pressure, and the action of solutions of one sort or another. Lewisian gneiss from northwest scotland, formed during the precambrian period, making it among the oldest rocks in the uk, pushed to the surface during an oregenic event, lewisian gneiss exhibits banded like most gneisses but is comprised of more dark, dense minerals, often igneous in origin. All structured data from the file and property namespaces is available under the creative commons cc0 license. Rather than an indication of specific mineral composition, the term is an indication of texture. The torridonian and moine sequences represent at least two main phases. Gneiss definition, a metamorphic rock, generally made up of bands that differ in color and composition, some bands being rich in feldspar and quartz, others rich in hornblende or mica. Many rocks were injected by a granitoid that has blue quartz and augen of potassic feldspar and are arteritic migmatites.
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