Textute of the mantle diamond-bearing rocks and crystal morphology of diamonds
Rakin V. I., Pomazansky B. S., Kovalchuk О. Е.
Zapiski RMO (Proceedings of the Russian Mineralogical Society). 2016. V. 145. N 4. P. 103-117
Full text is available
Language: Russian
Abstract
Fluctuations of the Gibbs free energy in equilibrium mantle rocks exceed the surface energy of an average grain. Therefore the texture of polymineral diamond-bearing mantle rocks can be represented as the foam-like texture with the cell surface areas which are exponentially distributed and coordination numbers of cells which are gamma distributed. For this texture, the mean coordination number is 15.7 with the standard deviation 11.4. Curie’s principle and textural parameters of mantle rocks were used to derive formulas of dis-symmetrization degree of diamond octahedron morphotypes. It is shown that this degree decreases with increase of the diamond crystal size. These formulas were also applied to explain the statistics of fine diamond fractions from Mir and Zapolyarnaya kimberlite pipes. In terms of the proposed model, the problem of the very long lasted growth story of natural diamonds, even on geological time scale, can be explained by the mechanism of a non-equilibrium crystallization during periods of increasing pressure due to activation of tectonic processes in the upper mantle.
Key words: mantle rocks, foam-like texture, diamond, octahedron, dis-symmetry, crystal growth.
