Plagioclase feldspar

Na[AlSi₃O₈]- Ca[Al₂Si₂O₈]

Plagioclase is a framework silicate in the feldspar group. Plagioclase is generally white with two distinctive cleavage planes at nearly right angles. Plagioclase can sometimes be distinguished from potassium feldspar by the presence of twinning which is visible as fine striations on the crystal faces. Plagioclase is commonly found igneous and metamophic rocks.