Defect and admixture composition of diamond crystals with growth pyramids <100> from placers of the Krasnovishersky district, the Urals
The internal structure of cuboid diamonds from contemporary alluvial placers of the Krasnovishersky district at the Urals was investigated with analyzing their spectroscopic characteristics. Crystals were divided into four groups by their anatomy and spectroscopic features: cuboids of the II variety in the Yu. L. Orlov classification; cuboids with transparent core and outer part saturated with inclusions; crystals with simultaneous growth of <100> and <111> pyramids, and crystals with their consecutive growth. The local photoluminescence investigations have been carried out for all different growth zones and pyramids. There was revealed localization of luminescence bands 926 and 933 nm to growth pyramids <100> and <111>. In all studied crystals, the last stage of growth was the regenerative formation of {111} face steps together with square pits forming on the surface. Some cuboids with C centres have specific luminescence systems, such as 575, 635.1, 636.8 nm, broad band with maximum at 700 nm, and intense lines at 800, 820.5, 840, 860, 869 nm. Different thermal history of mixed-habit diamonds was shown. It is noted that the cuboid diamonds from different regions of the world have the similar internal structure and spectroscopic features.