anorthoclase

The mineral anorthoclase ((Na,K)AlSi₃O₈) is a crystalline solid solution in the alkali feldspar series, in which the sodium-aluminium silicate member exists in larger proportion. It typically consists of between 10 and 36 percent of KAlSi₃O₈ and between 64 and 90 percent of NaAlSi₃O₈.