Notes on the Geology of Sule Stack, Orkney

Abstract

Sule Stack is composed of an orthogneiss traversed by shatter belts and small pegmatite veins composed of microcline and quartz. The chief constituent minerals of the gneiss are oligoclase and orthoclase felspars, hornblende altering towards chlorite, augite, and apatite. In addition some sections show magnetite and a few quartz. Comparisons are made between the gneiss of Sule Stack and that of the neighbouring island of Sule Skerry.