Gneiss Rock


Gneiss rock is easy to recognize.

It is a high-grade regional metamorphic rock with distinctive bands of minerals with different colours and sizes.





These rocks are folded even though the folds can sometimes be too large to see in a rock.

Like many metamorphic rocks they are foliated. They are, however, crystalline and not "schisty" - they do not break along layers as schists and some other metamorphics do.

 gneiss

The main minerals are quartz and feldspar. Others include mica, garnet, hornblende and staurolite.

 gneiss pictures
 By Rubem Porto Jr via Flickr.com 

Depending the mineralogy these rocks may have different colours such as gray, pink or others.

 gneisses
 By Richard Droker via Flickr.com

They often also have different names such as folded, biotite, or augen gneiss, depending on their texture or minerals.

 lewisian gneiss
 
By sparty lea via Flickr.com

They are medium to coarse grained.

 what is gneiss
 By Mike Beauregard via Flickr.com

They are formed at very high temperatures and pressures from rock such as siltstone, mudstone, shale and granitoids. They are used in building and pottery.













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