Abstract

The influence of ÑÎ2 and Í2Î on the morphology of diamond dissolution in carbonate melts was studied experimentally at pressure 5.7–7.0 GPa and temperature 1400–1750 °Ñ, using a BARS multi-anvil apparatus. It has been established that diamond dissolution in fluid-free carbonate melts starts with the development of positive trigons on the {111} diamond faces, followed by truncation of crystal edges by trigon-trioctahedral surfaces, and finally by the transformation of diamond into spherical dodecahedroid-like morphology. Diamond dissolution in ÑÎ2-bearing carbonate melts also begins with the formation of positive trigons on the {111} faces and development trigon-trioctahedron surfaces on the edges. Dissolution form changes from trigon-trioctahedron to dodecahedroid with increasing loss of initial weight. Addition of more than 8 wt% of Í2Î into the carbonate medium changes the orientation of the trigons and the secondary morphology of diamond. At the beginning of the process, negative trigons and ditrigonal (shield-shaped) dissolution layers developed on the {111} faces. Dissolution form of diamond in water-bearing melts is tetrahexahedroid, which is most similar to rounded natural diamonds. The results obtained allow us to regard the morphology of trigons and dissolution forms as an indicator of the composition of the diamond dissolution medium. The experiments suggest that the morphology of diamond during dissolution is controlled by the presence of water in a system. Our data show that the ÑÎ2/(ÑÎ2+Í2Î) ratio by weight value was <0.81 during natural diamond dissolution.

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