Growth morphology and change in growth conditions of a spinel-twinned natural diamond

Abstract Growth morphology appearing as external forms and zonal structures of spinel-twinned crystals of natural diamond from South Africa was studied. The crystals are divided into four groups depending upon the modification of their re-entrant corners by growth layers generated at the twin boundary. The flattened morphology is found to be caused by the preferential growth at both re-entrant and salient corners, the latter being revealed for the first time by this paper. The change of supersaturation conditions was also estimated from the morphological change.