2022
NF7202 : Lewisian gneiss outcrop
taken 2 years ago, near to Bruernish, Barra, Na h-Eileanan an Iar, Scotland
Lewisian gneiss outcrop
The Lewisian Gneiss, exposed in extensive glaciated outcrops at this location (see
NF7202 : Glaciated rock pavement) shows remarkable banded structure or foliation. This originates where the early-formed, pale granitic rock has been intruded by dark basaltic material and the composite then deformed in a more or less plastic state. Shearing has caused dark material to be stretched out in thin bands (top left) or thicker, more brittle blocks which have started to detach from each other. The last record is of transverse fractures which have been filled with new, quartz-rich mineralisation. This view is around 45 cms wide.
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