Anorthoclase

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