ИСТИНА

The diamonds from the Pioneerskaya kimberlite pipe were studied. At the upper horizons were established usual diamond crystals: round rhombododehedral (>2mm), octahedral and combination O-D forms (0,5-1mm), which are typical for kimberlites. At the depth were found unusual microcrystals (<0,1mm): hollow box skeletal round octahedron which irregular and incompletely filled by thin diamond plates, growing at the angle to the surface; tabular and crosslooked fragments of zone-sector crystals and the smooth licked grain in plating cover. Such types of crystals are similar to diamonds from metamorphic rocks of the Kokchetav massif in Kazakhstan and therefore we propose the similarity between conditions of there genesis. The experimental data shows, that such crystals are characterized by fibrous mechanism of growth, which takes place at unequilibrium conditions when temperature decreases. The result of such deviation from equilibrium may be spherical isometric forms of diamonds. Skeletal growth of crystals are due to fast deposition of carbon, sharp increasing of saturation degree and high content of impurities. The impurities increase the speed of growth and make the diamond crystals defective and they acquires sector and zone-sector structure. Fast saturation (cooling) of mineral solution is the cause of forming a great number of nucleos, that explains a very small size of diamond crystals and the wide spreading of twins.