bytownite
bytownite
A triclinic mineral, (Ca,Na)[Al,Si)AlSi2O8] having 90 to 70 mol % Ca and 10 to 30 mol % Na; of the plagioclase series of the feldspar group; prismatic cleavage; white to gray; forms phenocrysts in some basalts and layered mafic-ultramafic intrusions