EVOLUTION OF GROWTH SECTORS IN NATURAL DIAMOND CRYSTALS AS REVEALED BY CATHODOLUMINESCENCE TOPOGRAPHY

Abstract

Plates cut from natural diamond crystals from the Siberian diamondiferous province were studied using an optical microscope and scanning electron microscope equipped with a color TV display. Many crystals exhibit a change in the development of octahedral {111} and cubic {100} growth sectors. Most such diamonds showed abundant cubic sectors at the first growth stage and only octahedral sectors at the final stage. Diamond crystals with the opposite evolution were rather rare. Some other types of growth sector evolution were found. In particular, the following unusual oscillatory change of forms was revealed: a rounded inoculation → {100} → {111} → {100} + {111} → {111}. Various luminescence types related to different structural defects were found in the cubic growth sectors. Published data on growth sectors in natural diamond crystals were summarized, and a general crystal morphology series of diamonds from kimberlites was developed. On the basis of our results and data on growth sectors in diamonds synthesized under various conditions, it was suggested that temperature was the main factor controlling the development of various growth sectors in natural diamond crystals, and a temperature rise was the main tendency during the diamond growth in nature. The temperature rise is consistent with the hypothesis of diamond formation as a result of inflow of deep-seated hydrocarbon fluids into the lithosphere.