Crystal System: Triclinic
Status of Occurrence: Unconfirmed Occurrence
Distribution: Uncommon
Chemical Composition: Sodium potassium aluminium silicate
Chemical Formula: (Na,K)AlSi3O8
Method(s) of Verification: none.

Chemical Group:

  • Silicates
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.

Key Localities:

There are no key localities for this specimen.


  1. Greenly, E., 1919. The Geology of Anglesey. Memoirs of the Geological Survey of Great Britain, 980pp (2 volumes).

There are no references for this specimen.