Gneiss

© Craven & Pendle Geological Society

Augen Gneiss from north Scotland

Augen Gneiss

Summary:
Gneiss is a medium to coarse-grained banded rock formed as a result of high grade regional metamorphism.  It is characterised by a layered appearance caused by the segregation of ferromagnesian minerals from quartzo-feldspathic minerals in discontinuous layers.  The ferromagnesian minerals are commonly biotite and/or hornblende with pyroxene being less common.  Garnet is often present as an accessory mineral.

Augen gneiss is characterised by very coarse-grained eye-shaped lenticles of quartz and feldspar.

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