Growth Spirals and their Relation to Crystal Habit as Illustrated by Apatite

Abstract

THE observation of growth spirals, as predicted by the theory of Burton, Cabrera and Frank¹, on prism faces (10&1bar;0) of apatite crystals, has been reported earlier². We have now observed completely differently shaped growth spiral patterns on tabular colourless apatite crystals from Sulzbachtal (Austria), which have probably grown from solution. The accompanying photograph (Fig. 1) shows one of the observed patterns. The direction of the c-axis is vertical. The shape and orientation of the spiral are the same in all cases. The dominating system consists of two co-operating spirals, which dominate several other dislocations of equal and of different strengths. In the latter case the formation of residual steps is noticed. Interlacing occurs in one direction. The main growth-fronts have a step-height of 140 ±.20 A.