Abstract
It is well known that twinned crystals exhibit morphological characteristics which are different from those of the o-existing single crystals. They are summarized in four characteristics; (1) more flattened morphology than single crystals, (2) larger size than single crystals, (3) appearance of faces uncommon for single crystals, and (4) less kind of crystal faces. These characteristics have been accounted for in terms of re-entrant corner effect at twin junctions. The validity of this explanation is critically investigated based on a model of crystals containing imperfections. For real crystals, these morphological characteristics can appear only when crystals grow under low supersaturation and contain more dislocations in the twin boundary than the surface. Morphological characteristics of twinned crystals (examples : quartz twins after Japan Law, spinel twins of diamond, Ge ribbon crystals) are analyzed on the new model.
