Movement of screw dislocations in hematite.(With Plates I and II.)

Abstract

Summary The surface structure of the basal pinacoid of crystals of hematite has been studied by phase contrast microscopy, yielding evidence of the movement of dislocations after the cessation of growth. Steps due to such movement are initiated from the centre of growth spirals, and cross the growth fronts without interrupting the growth layers. Viewed from the dislocation the step has the higher side on the left for right-handed spirals and vice versa. In the majority of cases the step is straight, but rarely it is curved or kinked. It is proposed to call such steps ‘dislocation scarps’. The number and length of dislocation scarps vary considerably in crystals from different localities. These variations probably reflect differences in the stress history of the crystals.