The internal structure of microdiamonds from the Udachnaya kimberlite pipe

For reconstructing formation conditions, the internal and real structures o f microdiamonds from the Udachnaya kimberlite pipe were studied by the meth ods of X-ray and cathode-luminescent topographies and IR spectroscopy. One of the main elements of the internal irregularity of most microcrystals Is a linear or a step-like zoning along {111}. Structurally, most microdia monds have several domains significantly differing in physical characterist ics. It is established that the periphery of microdiamond crystal always ha s more A-type defects than B1-type ones. Such specific features are most ob vious in octahedral microcrystals. Rounded microcrystals may have disturbed primary-growth features as a result of their longer stay in the deep mediu m. It has been revealed that cubic microcrystals have subparallel filaments (with a small disordering angle), which are a sign of a normal growth mech anism. This mechanism is realized owing to the higher degree of oversaturat ion in the crystallization medium as compared with the layer-by-layer growt h mechanism. Some cuboids have central zones saturated with discrete microi nclusions of water and carbonates, which indicates the presence of a water- carbonate fluid at the initial stages of the formation of such crystals. The obtained data suggest that the microdiamond formation passes through se veral stages. The alteration trend for some physical characteristics may be st sign of the re:gular evolution of the Udachnaya-pipe microdiamonds.