the other crystal structure or polymorph of zinc sulphide, the sulphur atoms are stacked in the hexagonal ABABAB... sequence, giving a hexagonal structure. In both cases the zinc atoms occupy half the tetrahedral interstitial sites between the sulphur atoms. As in the case of cobalt, stacking faults may arise during crystal growth or under conditions of deformation, giving rise to 'mixed' sphalerite-wurtzite structures.