Introduction: anorthoclase is member of the feldspar group, more specifically the orthoclase feldspars, and is a rock-forming mineral. It most commonly occurs in high temperature sodic volcanic and high level intrusive rocks

Occurrence in Wales: the only reported occurrence of anorthoclase from Wales is provided by Greenly (1919) who described anorthoclase with albite in a folded pegmatitic quartz augen within the Gwna Group schists exposed in the vicinity of Craig-y-don house, near Menai, Anglesey. These schists formed under low temperature (probably less than 300°C) metamorphic conditions which are not consistent with the conditions of formation of anorthoclase. This reported occurrence must therefore be treated as a suspected misidentification.

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