The common pseudo-hexagonal polysynthetic twinning of cubanite will occur when cubic cubanite crystallizes at the temperature higher than about 220°C and transforms to the orthorhombic low form as lowering of temperature. The twinnings of cubanite and coexisting chalcopyrite of Omine mine were examined by x-ray single crystal diffraction methods.
Some cubanite crystals (sample nos. 24 and 9) were single crystals containing small amount of chalcopyrite lamellae with {112} polysynethetic twinnings. The other common cubanites, which occur as narrow lamellae in the chalcopyrite host, had polysynthetic caxis rotation twinnings, and the chalcopyrite had {110} contact polysynthetic twinnings. Cubanite without twinning is considered to have been crystallized initially as the low orthorhombic form.