Diamond Crystallization at High Pressure: The Relative Efficiency of Metal-Graphite and Metal-Carbonate Systems

Data on the interaction of the Fe–Ni melt with CaCO 3 and graphite at 5 GPa and 1400°С under the thermogradient conditions used in experiments on the growth of diamond on the BARS high-pressure apparatus are presented. The phase composition and component composition of the fluid captured by diamonds in the form of inclusions were studied by gas chromatography–mass spectrometry (GC–MS). Diamonds were synthesized from graphite. During the interaction of the Fe–Ni melt with CaCO 3 , Ca–Fe oxides and (Fe, Ni) 3 C carbide were formed. The stability of heavy hydrocarbons under the experimental conditions was confirmed. It was established that the composition of the fluid in synthesized diamonds is close to the composition of the fluid from inclusions in some natural diamonds. Nevertheless, it was concluded that crystallization of large diamonds under natural conditions is hardly possible due to the filling of the main crystallization volume with refractory oxide phases.