We have investigated the kinetics of twinning in diphenyl crystals and the external morphology of diphenyl, quartz and flourphlogopite crystals. It has been shown that under definite crystallization temperature, interval of supercooling of melts and supersaturation of vapour or solutions, a zone of faces forms on crystals. Over these faces individual crystals grow in the twinned orientation. The growth twinning is epitaxial in nature. Twinning epitaxy is a widely popular phenomena in natural and synthetic crystals. The primary inclusions are responsible for the self-reorientationof the crystals obtained by Czochralski and directional crystallization methods.