It was recalled that single crystals of natural diamond which exhibited an approximately cubic morphology were known to have grown either via non-faceted cuboid growth or via fibrous growth which branched into a multiplicity of <111> columns, to give a mean surface orientation of {100}. It was noted that interpenetrating twins in diamond were not common but, when they occurred, they were usually coloured and appeared (in X-ray topographs) to have been formed by fibrous growth from a twin origin, with the 14 growth sectors adequately filled by fibres, without any need for branching.

Twinning in Natural Diamond - II: Interpenetrant Cubes. W.G.Machado, M.Moore, A.Yacoot: Journal of Applied Crystallography, 1998, 31[5], 777-82