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A pink-purple diamond crystal from the Internatsional'naya kimberlite pipe (Siberia) was studied by single-crystal X-ray diffraction techniques using an area detector. Direct indexing of the diffraction pattern suggested a primitive hexagonal unit cell [ahex = 2.513(4), chex = 6.172(11) Å], instead of the well known face-centred cubic unit cell (acub ∼3.567 Å). Theoretical considerations and diffraction pattern simulation showed that the hexagonal diffraction pattern is the result of the superposition of two diffraction patterns with cubic symmetry due to spinel-law twinning along (111). These data are in good agreement with previous analyses of deformation microtwins in natural pink-purple diamonds using electron paramagnetic resonance spectroscopy and optical microscopy. The results suggest that natural epigenetic plastic deformation of diamonds occurs not only by dislocation slipping but also as a result of mechanical twinning.

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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 between 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.