Rounded diamond crystals with mixed growth mechanism from alluvial placers of the Krasnovishersky district, the Urals

Vasiliev E. A., Klepikov I. V., Antonov A. V.

Zapiski RMO (Proceedings of the Russian Mineralogical Society). 2018. V. 147. N 4. P. 114-126

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Language: Russian


Internal structure and spectroscopic characteristics were studied for two rounded diamond crystals with relicts of cube faces from contemporary alluvial placers of the Krasnovishersky district (the Urals). The share of nitrogen in form of B1 defects in these crystals reaches 70 %. These two stones represent two types of diamond: one with a joint and another with successively changing growth of cube and octahedron faces. The relatively joint development of faces of a cube and an octahedron at different stages determined the change from a cube to a skeleton cube and a cuboctahedron. It is shown that in the crystal with a successive change of the growth mechanism, the growth temperature of the cubic zone was higher than temperature of the octahedral zones growth. The peripheral part of both crystals is composed of flat zones with a tangential growth along the common direction of the {100} faces. The growth temperature at this stage has decreased, as follows from the distribution of the «platelets» size. The presence of several dissolution boundaries with subsequent regeneration in the crystal shows that dissolution occurred at the threshold of the thermodynamic stability of a diamond.

Key words: diamond, the Urals, morphology, internal structure, FTIR, photoluminescence, mixed-habit growth.