DEFECTS IN CUBIC DIAMONDS FROM THE PLACERS IN THE NORTHEASTERN SIBERIAN PLATFORM: RESULTS OF IR MICROSPECTROMETRY
Defects in yellowish-green, yellow, and orange diamonds of cubic habit from placers of the northeastern Siberian Platform were studied by IR spectroscopy. In addition to the main A, C, and, probably, B defects, the diamonds contain X and Y centers and amber defects of different types and show absorption bands at 1240, 1270, and 1290-1295 cm-1, peaks in the region 1350-1380 cm-1, and bands within 3100-3300 cm-1. Diamonds of different colors contain different associations of structural defects, though they belong to the same variety II according to the Orlov classification. According to the integral spectra of the diamond crystals, the content of structural nitrogen impurity is low, 60-265 ppm. However, spatially resolved spectroscopic examination of diamond plates has revealed highly nonuniform distribution of defects in all diamond crystals. The general regularity for the studied diamonds is a decrease in the total nitrogen content and in the relative fraction of the major A defect from core to periphery of a crystal. The content of structural nitrogen impurity in the core reaches 900 ppm, which is higher than the average N content in widespread octahedral diamond crystals. The presence of C, Y, and X defects in the majority of the samples indicates short postgrowth annealing of these diamonds. The genetic significance of the obtained data on structural defects is discussed.