It was recalled that it had become automatic to equate the observation of a growth spiral to the existence of a screw dislocation in the growing material. It was noted here that there was a need to distinguish carefully between the nature of the dislocation and the mono-step topology which developed during growth at the dislocation. In particular it was noted that, although an edge dislocation could not form a growth step on a surface where its Burgers vector was parallel to the face, steps (and therefore spirals) could nevertheless form on side-faces that were parallel to the line of the edge dislocation.

Edge Dislocations and Growth Spirals. H.P.Strunk: Journal of Crystal Growth, 1996, 160, 184-5