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lamellar In crystallography, applied to a special kind of crystal twinning (also called ‘multiple’ or ‘repeated’ twinning) where there are many twin individuals, each one having a tabular or plate-like appearance. Lamellar twinning is common within the plagioclase feldspars, in places where two adjoining twin slabs or lamellae are mutually reversed with respect to each other and every alternate twin ‘plate’ or ‘slab’ has an identical atomic structure.