Relationship between crystal morphology and twin boundary structures of quartz twinned in accordance with Japan law

Twinned crystals often grow larger and/or in diŠerent morphologies than coexisting single crystals. Such characteristics of twinned crystals are generally explained as a result of `reentrant corner eŠect'. However, observations of natural quartz crystals twinned in accordance with Japan law and computational simulations on the twin boundary structures revealed more complex growth mechanism, in which formation of dense Brazil twin lamellae at the {112̃2} composition plane of Japanese twin boundary causes the preferential growth of Japanese twin. The intersections of Brazil and Japanese twin boundaries were found to be structurally coherent when they have certain composition planes. This structural diversity of the {112̃2} Japanese twin boundaries causes development of ˆne Brazil twin lamellae and triggers faster growth.