ИСТИНА

Morphology and physical properties for around 2000 diamonds have been examined from Arkhangelsk kimberlites and different placers. The proportions of external forms vary between hosts. The rhombododecahedra dominate (35,5-70%) in all cases, but aggregates are abundant in the North Yakutian placers (25,5-35,5%). Transition O-D crystals are the second in abundance (9,1-29,4%). More than a half of them have >2mm sizes. Octahedra are at the third place (2,3 - 15,5%). The most of them are attributed to the +0.5-1.0 mm size class. The content of cubic crystals is low (5,9-28,9%). The degree of resorption evident in each suite are high. Knob - like asperities, ribbing, frosting, corrosion sculptures, etch channels and lamination lines are well developed on many of the crystals. Most of them reflected the deformation, resorption and late-stage processes. Almost all studied diamond crystals are attributed to the Ia type. It means, that they contain essentially nitrogen defects. Predominant in all suites are colorless diamonds. Their spectrums have absorption edge at 300 nm, and contain characteristic series of lines: N2, N3, N4, which correspond to the A and B type defect existence. The content of the II type diamonds is low (1-2%). They have a spectrum with absorption edge 225 nm, series N2, N3, N4 are absent. Among colored polyhedra grey crystals are the most abundant, brown and smoky-brown are less developed. Yellow individs are uncommon. They all have spectrum stipulated for the intense short-wave absorption and wide lines at 475, 500 and 700 nm, connected with plastic deformation of the crystals and existence of C defects. The studying of diamond helped to reveal typomorphism of morphology and physical properties of diamonds from investigated hosts. The prevalence of rounded rhombododecahedra for diamond is established in comparison with the crystals from South Jakutia and South Africa, where the octahedra are the predominant primary form. Studied diamonds, on average, show slightly higher nitrogen content than the crystals from South Jakutia and South Africa pipes. A higher proportion of diamonds from investigated hosts relative to South Yakutian kimberlites are heavily frosted and contain etch channels. The established trends may relate to variations in the physical-chemical conditions of the growth environments.