The plagioclase feldspars, particularly albite (NaAlSi₃O₈), are frequently twinned on the albite law (see twin law) where the twin plane and composition plane is (010). This twinning is often repeated to give a series of fine lamellae, seen in the hand specimens as striations (particularly on the basal plane); such twinning is usually called ‘polysynthetic’ or ‘lamellar’ twinning.