On the internal structure of natural diamonds of cubic habit

Abstract

Abstract Three natural cubes, each of edge length about 1·8 mm. were examined by x-ray topography. Two possessed very similar internal structures, describable in terms of space-filling by fibrous or columnar single-crystal growth in <111> directions, with branching and equal growth velocities in these symmetrically equivalent directions. On a microscopic scale this structure appears similar to that of diamond coat: the cubic habit results from the branching mode of growth when the final crystal size is large compared with the dimensions of its core or nucleus. The internal structure of the third cube was entirely different. The record of growth horizons and dislocation trajectories showed that during most stages of its growth it had developed with a combination of forms: normal {111} faces plus hummocky, non-crystallographic surfaces of mean orientation {100}. The latter had become dominant in the outer parts of the crystal but the final overall cubic shape had been accentuated by solution following growth.