Coarse Outer Granite away from contact, near Glen Catacol (Hunterian Museum rock number AH4138)

This is from near Creagan nan Gohhar to the south of Glen Catacol. This is typical granite: it is quite coarse-grained: only a few grains fit into the field of view of the microscope.. It consists mainly of alkali feldspar, plagioclase feldspar (hard to tell apart in this view, both rather cloudy), and quartz . Between crossed polars, the quartz and feldspars show low order grey colours: the plagioclase shows typical striped lamellar twinning, while the alkali feldspar shows patchy perthitic texture.

Courtesy of Dr John Faithful