Analysis of an unusual mixed-habit natural diamond by high spatial resolution techniques: Growth and fracture

Mixed-habit growth of natural diamond is relatively uncommon and the reasons why it occurs are not well-understood. The diamond studied here, unusually, alternated between cuboidal and octahedral growth over a very long period making it possible, using a variety of high resolution analytical techniques, to establish the properties of the different phases of growth. In particular, nickel, in the form of NE centres, was restricted the cuboidal regions which also contained very high levels of hydrogen. There was a high concentration of nitrogen in the sample, but photoluminescence microscopy revealed it was incorporated in the two different regions of growth in very different forms with strong N3 emission from the octahedral regions, but in the hydrogen-related 3107 cm−1 infra-red and NE centres in the cuboidal regions. These results suggest that the traditional means of assaying nitrogen levels by A- and B-centre absorption may require additions. The section of the sample studied was quite close to the nucleation of growth and study of this region by high spatial resolution photo- and cathodoluminescence microscopy revealed previously unreported aspects of this critical growth step. The experimental results also indicate that a major fracture occurred with new diamond grown between the mixed-habit and the later octahedral growth.