Effect of diamond growth rate on carbon isotope fractionation in Fe-Ni-C system

The carbon isotope fractionation factor between diamond and carbon dissolved in the Fe-Ni metal melt varies from 4.1 parts per thousand down to 2.4 parts per thousand in HTHP crystallization experiments with the average diamond growth rates ranging from 1 to 12.5 mg/h. The observed fractionation of heavy carbon isotope is in agreement with the Burton-Prim-Slichter model for the compatible impurity distribution associated with crystallization. The variations in the carbon isotope composition within a single diamond crystal can result from appropriate variations of the crystal growth rate. The scale of the observed fractionation effect is comparable with the internal isotope inhomogeneity of natural stones. (C) 2011 Elsevier B.V. All rights reserved.