X-ray Bragg reflexion, ‘spike’ reflexion and ultra-violet absorption topographic studies of internal structures of natural dimonds revealing mixed-habit growth

Abstract

Certain diamonds have had epochs of simultaneous growth on normal {111} octahedral faces and on non-f acetted, hummocky surfaces of mean cube orientation (Cuboid surfaces) . Such diamonds are called“Centre-cross diamonds”. Centre-cross patterns are obtainable only when octahedral and Cuboid growth forms are symmetrically and approximately equally developed. As a first step to establish the chemical identity and the state of the habit modifiers which induce Cuboid growth, we have made a reconnaissance of the variety of manifestations of Cuboid growth, as exhibited in a suite of diamonds selected for visible evidence of centre-cross structure. Such threedimentional investigations are fittingly performed by x-ray topography. X-ray topographs of 11 diamonds are analysed to illustrate the wide range of relative development these two growth forms can exhibit and the variations in content of imperfections, both microscopic and sub-microscopic, in such crystals.