Morphology of Crystals Growing in Impact Diamonds of the Popigai Astrobleme (Experimental Data)

Experimental results on the growth of cubic diamond on lonsdaleite-bearing diamonds from the Popigai astrobleme at 5.5 GPa and 1450°C in the Fe–Ni–C system are presented. Due to the simultaneous appearance of several crystallization centers, the cubic diamond phase occurred in the form of an aggregate. This is probably due to the specific structure of the paracrystals of impact diamonds from nanosized crystallites (10–100 nm) or polysynthetic twinning inherited from graphite crystals under ultrahigh pressure. The color of the diamond crystals is yellow and is typical of diamonds grown in the Fe–Ni–C system. The predominant morphological shape of diamond crystals is octahedra with additional cubic, rhombic dodecahedron, and tetragonal-trioctahedra faces.