MICRODIAMONDS FROM THE UDACHNAYA KIMBERLITE PIPE

The paper considers a variety of microdiamonds (<1 mm) from the Udachn aya kimberlite pipe both by morphology and the content of nitrogen def ects. By the ratio of the main morphological types, they are character ized by a significant increase in the amount of dodecahedroids and cub oids as compared with macrodiamonds. The microcrystals without dissolu tion signs also show a wide variety of simple forms. Spectroscopic stu dy of the microdiamonds has shown that the predominant forms of nitrog en incorporation are A and B1. The amount of the C-defects is insignif icant. Many crystals contain hydrogen as an impurity. By means of cath ode luminescence, a zonal structure of some microcrystals has been est ablished. The microdiamonds of different morphology differ in the rati o of impurity sites. Using an ''annealing'' model of nitrogen aggregat ion, it is possible to establish a difference in the time-temperature characteristics of particular groups of microdiamonds. The considered differences of the revealed microdiamond groups and the differences in the distribution of the morphological types of the micro- and macrodi amonds from the Udachnaya pipe may be an indicator of the time-spatial irregularity of the diamond formation conditions. But, taking into ac count the uncertainty of some parameters, it is still impossible to un ambiguously determine the time and site of microdiamond crystallizatio n in kimberlites.