Composition Of Granite Gneiss

Orthogneiss is gneiss derived from igneous rock such as granite.

Composition of granite gneiss.

These bands are usually light in color and alternate with bands of darker colored minerals with platy or elongate habits. Chemical composition of gneiss gneissic rocks are usually medium to coarse foliated. Pink k feldspar gray quartz and black biotite. 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.

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. It was originally a mining term meaning a country rock in the ore mountains erzgebirge which contained metalliferous veins. They are largely recrystallized but do no longer deliver large quantities of micas chlorite or different platy minerals. Gneiss is formed by high temperature and high pressure metamorphic processes acting on formations composed of igneous or sedimentary rocks.

The term gneiss was brought to scientific usage from the german language. Gneiss metamorphic rock that has a distinct banding which is apparent in hand specimen or on a microscopic scale. Gneiss usually is distinguished from schist by its foliation and schistosity. Gneiss is made up of coarse grained minerals such as quartz and feldspar.

For the casual student it is convenient to think of a gneiss as a rock with parallel somewhat irregular. This specimen has a composition of an ordinary granite. The main difference between gneiss and granite is that gneiss is a type of metamorphic rock whereas granite is a type of igneous rock. Width of sample 11 cm.

Gneiss is a high grade metamorphic rock having many of the aerial photograph characteristics of granite. In fact primary gneiss is largely indistinguishable from granite at aerial photograph scales. Gneisses which can be metamorphosed igneous rocks or their equivalent are termed granite gneisses diorite gneisses and so on. Granite gneiss definition is a rock consisting of an orthogneiss or paragneiss having the composition of a granite.

There are three major types of rocks as sedimentary rocks igneous rocks and metamorphic rocks. Ortho gneiss is essentially metamorphosed granite so it too is similar in appearance to granite. It is a step above gneiss in the metamorphic process meaning schist has been subjected to less intense heat and pressure. Schist is a metamorphic rock usually formed originally from shale.

Paragneiss is gneiss derived from sedimentary rock such as sandstone. Gneiss displays a well developed foliation and a poorly developed schistosity and cleavage. Gneiss forms at higher temperatures and pressures than schist.