Saturday, 4 April 2015

Gneiss

Gneiss
Gneiss is a high grade metamorphic rock which has been subjected to high pressure and temperature formed from the pre-existing rocks either from the igneous or sedimentary rock. Gneiss is composed of foliation which is represented by bands of dark and light colour. In gneiss less than 50% of minerals are aligned in thin foliated layers and unlike slate and schist, it does not break along planes of foliation. 

Gneiss is associated with mountain building (orogeny)

Gneiss is associated with major mountain building events. In these events sedimentary or felsic igneous rocks are subjected to high pressure and temperature from the great burial depths, igneous intrusions and tectonic forces generated in these events. 

Composition of gneiss

Gneiss is composed of felsic minerals such as felspar (orthoclase and plagioclase) and quartz from the light coloured bands. From the dark coloured bands mafic minerals are present such as biotite, pyroxene and amphibole.

Grains of gneiss

Grains of gneiss are medium to coarse grained, crystals large enough to be seen with naked eye.

Uses of gneiss

Gneiss is a hard metamorphic rock because of the forming from high pressure and temperature. It can be used as a dimension stone by making slabs and square shape. It can also be used in construction as pavement, crush in roads etc.

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