Chemical Composition Of Granite Gneiss

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.

Chemical composition of granite gneiss.

Pink k feldspar gray quartz and. Gneiss is a medium to coarse grained semischistose metamorphic rock. The main difference between gneiss and granite is that gneiss is a type of metamorphic rock whereas granite is a type of igneous rock. Augen gneiss from the german.

Depending on its chemical composition granite has specific geological petrographic names which are all grouped under the generic heading of granite. Rocks are naturally occurring solid masses or aggregates of minerals there are three major types of rocks as sedimentary rocks igneous rocks and metamorphic rocks. Average chemical composition of granite determined by 2485 chemical analyses of granitic rocks 3 numbers are mass percents recalculated volatile free to total 100. Gneiss is a very widespread rock type especially in the lower parts of the continental crust but it is also a common rock on the surface in some places scandinavia canada and other shield areas where crystalline rocks are not covered by a layer of sedimentary rocks.

The random arrangement of grains in granite its lack of fabric is evidence of its plutonic origin. This specimen has a composition of an ordinary granite. It can also contain layers of quartz known as gneiss. Other bands contain platy or elongate minerals with evidence of preferred orientation.

Density melting point. A contact between gneiss granodioritic with migmatitic granite veins and granite pegmatite. Orthogneiss is formed by the metamorphism of igneous rocks. It is this banded appearance and texture rather than composition that define a gneiss.

A sample from karelia russia. But that kind of rock has a strong fabric and is usually called granite gneiss. It is characterized by alternating light and dark bands differing in mineral composition coarser grained than schist. Paragneiss results from the metamorphism of sedimentary rocks.

Paragneiss is gneiss derived from sedimentary rock such as sandstone. The lighter bands contain mostly quartz and feldspar the darker often contain biotite hornblende garnet or graphite. 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. Sio 2 71 84 tio 2 0 31 al 2 o 3 14 43 fe 2 o.

Gneiss can be classified on the basis of minerals that are present presumed formational processes chemical composition or probable parent material. Granite comes in many different guises from a very fine and dense grain to a coarse grain.