Anorthoclase

Anorthoclase is a crystalline solid solution in the alkali feldspar series, with the sodium-aluminium silicate member exceeding the potassium-aluminium silicate member. It typically consists of 64 to 90 percent NaAlSi3O8 and 10 to 36 percent KAlSi3O8. The mineral is an intermediate member of the high albite–sanidine series, stable at temperatures of 600 °C and above, and exhibits triclinic symmetry.