Experimental and Theoretical Evidence for Surface-Induced Carbon and Nitrogen Fractionation during Diamond Crystallization at High Temperatures and High Pressures

Crystals

Michael Wiedenbeck¹  EIMF²  Piotr M. Kowalski³  Yury N. Palyanov⁴  Vadim N. Reutsky⁴ 

[1] Deutsches GeoForschungZentrum, 14473 Potsdam, Germany;Edinburgh Ion Microprobe Facility, Grant Institute of Earth Sciences, School of GeoSciences, University of Edinburgh, Edinburgh EH9 3JW, UK;Institute of Energy and Climate Research (IEK-6), Forschungszentrum Juelich, 52425 Juelich, Germany;Sobolev Institute of Geology and Mineralogy SB RAS, Novosibirsk 630090, Russia;

关键词: mixed-habit diamond crystallization;    carbon isotopes;    nitrogen impurity;    fractionation;    experiment;    high pressure;    high temperature;    crystal chemistry;    surface structure;    SIMS;   

DOI  :  10.3390/cryst7070190

来源: DOAJ

【 摘 要 】

Isotopic and trace element variations within single diamond crystals are widely known from both natural stones and synthetic crystals. A number of processes can produce variations in carbon isotope composition and nitrogen abundance in the course of diamond crystallization. Here, we present evidence of carbon and nitrogen fractionation related to the growing surfaces of a diamond. We document that difference in the carbon isotope composition between cubic and octahedral growth sectors is solvent-dependent and varies from 0.7‰ in a carbonate system to 0.4‰ in a metal-carbon system. Ab initio calculations suggest up to 4‰ instantaneous 13C depletion of cubic faces in comparison to octahedral faces when grown simultaneously. Cubic growth sectors always have lower nitrogen abundance in comparison to octahedral sectors within synthetic diamond crystals in both carbonate and metal-carbon systems. The stability of any particular growth faces of a diamond crystal depends upon the degree of carbon association in the solution. Octahedron is the dominant form in a high-associated solution while the cube is the dominant form in a low-associated solution. Fine-scale data from natural crystals potentially can provide information on the form of carbon, which was present in the growth media.

【 授权许可】

Unknown