In The Formation Of Gneiss From Granite T

Granite is an intrusive igneous rock which is very hard crystalline and is visibly homogeneous in texture and forms by melting of continental rocks gneiss is a high grade metamorphic rock i e.

In the formation of gneiss from granite t.

Augen gneiss from the german. Paragneiss is gneiss derived from sedimentary rock such as sandstone. It has been subjected to higher temperatures and pressures than schist. Granite is a very hard granular crystalline igneous rock which consists mainly of quartz mica and feldspar and is often used as building stone gneiss is a common and widely distributed type of rock formed by high grade regional metamorphic processes from pre existing formations that were originally either igneous or sedimentary rocks.

These temperatures cause the individual minerals to migrate forming distinct bands through the rock. 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. Formation high temperature and high pressure processes that act on igneous and sedimentary rocks cause the formation of gneiss while the slow crystallization of magma forms granite. Granite gneiss can also form through the metamorphism of sedimentary rocks.

In simplified terms you can think of gneiss as a metamorphic version of granite. Gneiss is formed from the high temperature metamorphism of existing igneous rocks generally granite or diorite. The mineral composition of both granite and gneiss is same but alteration of granite because of very high pressure and temperature leads to the formation of gneiss. The rocks that form gneiss are exposed to extreme pressures and temperatures of between 600 and 700 degrees celsius.

Both gneiss and granite are made of feldspars quartz mica and smaller amounts of dark colored minerals like hornblende. Augen which means eyes is a coarse grained gneiss because of metamorphism of granite which incorporates characteristic elliptic or lenticular shear bound feldspar porphyroclasts typically microcline within the layering of the quartz biotite and magnetite bands. Intense heat and pressure can also metamorphose granite into a banded rock known as granite gneiss this transformation is usually more of a structural change than a mineralogical transformation.