Deformation twinning in corundum

Abstract

Abstract Deformation twinning on rhombohedral planes was detected in corundum crystals fractured in bending at temperatures as low as − 196°c. The crystallographic parameters of this twinning were determined completely: s=0·202. Deformation markings, tentatively attributed to basal twinning, were detected on some crystals fractured above 1000°c. Twins were observed to be associated with fracture faces, and in some cases twin-sub-grain and twin-twin intersections, which probably nucleated fracture, could be found.