albite twin

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albite twin 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.