Composition Of Granite Gneiss

Gneiss usually is distinguished from schist by its foliation and schistosity.

Composition of granite gneiss.

Gneiss metamorphic rock that has a distinct banding which is apparent in hand specimen or on a microscopic scale. The main difference between gneiss and granite is that gneiss is a type of metamorphic rock whereas granite is a type of igneous rock. There are three major types of rocks as sedimentary rocks igneous rocks and metamorphic rocks. Gneiss forms at higher temperatures and pressures than schist.

The term gneiss was brought to scientific usage from the german language. This specimen has a composition of an ordinary granite. This is a rock that is formed from pre existing igneous rocks such as granite that have been subject to conditions of high pressure and temperature. Width of sample 11 cm.

Chemical composition of gneiss gneissic rocks are usually medium to coarse foliated. Gneiss is a high grade metamorphic rock having many of the aerial photograph characteristics of granite. Gneiss is made up of coarse grained minerals such as quartz and feldspar. Rocks are naturally occurring solid masses or aggregates of minerals.

It was originally a mining term meaning a country rock in the ore mountains erzgebirge which contained metalliferous veins. Gneiss displays a well developed foliation and a poorly developed schistosity and cleavage. They are largely recrystallized but do no longer deliver large quantities of micas chlorite or different platy minerals. Granitic gneiss has a mineral composition similar to that of granite.

Schist is a metamorphic rock usually formed originally from shale. Gneisses which can be metamorphosed igneous rocks or their equivalent are termed granite gneisses diorite gneisses and so on. Orthogneiss is gneiss derived from igneous rock such as granite. Gneiss is a hard rock that has a mineral composition similar to granite as it contains the feldspar mica and quartz.

Granite gneiss definition is a rock consisting of an orthogneiss or paragneiss having the composition of a granite. Gneiss is formed by high temperature and high pressure metamorphic processes acting on formations composed of igneous or sedimentary rocks. In fact primary gneiss is largely indistinguishable from granite at aerial photograph scales. 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.

These bands are usually light in color and alternate with bands of darker colored minerals with platy or elongate habits. Pink k feldspar gray quartz and black biotite. Paragneiss is gneiss derived from sedimentary rock such as sandstone.