Variability of conditions of natural diamond formation based on data on the distribution of structural impurities in the volume of diamond crystals

Based on a large-scale study of the distribution of structural impurities in the volume of diamond crystals from pipes and placers in different regions of the world, the relationship between the crystal growth forms and the temperature of their formation is shown. Octahedral diamonds were formed in the highest-temperature and deepest conditions, and cubic diamonds – in relatively low-temperature and shallowest conditions, near the diamond-graphite equilibrium. In the cube-octahedron series, diamonds with a change in the growth mechanism are in an intermediate position. Crystals with a change in the octahedron → cube growth forms, common among Arkhangelsk diamonds (Lomonosov deposit), were formed mainly as a result of a decrease in temperature and with an excess of the hydrocarbon source of the diamond substance throughout its growth. Crystals with a change in the cube → cuboctahedron → octahedron growth forms, typical for Yakutia deposits, were formed in a relatively narrow temperature range, but with a significant decrease in the concentration of hydrocarbons in the medium at the final stage of growth.