DIAMOND FORMATION DURING REDUCTION OF OXIDE- AND SILICATE-CARBON SYSTEMS AT HIGH P-T CONDITIONS

Abstract

Although it is accepted that most natural diamonds crystallized from silicate melts, and P-T conditions of their formation are estimated to be 900-1500°C and 50-60 kbar, no diamonds have been synthesized at such 'low' temperatures and pressures in silicate-carbon systems. We have synthesized diamonds in fayalite+graphite and magnetite+graphite mixtures by partial reduction of the samples with hydrogen and metallic titanium at 1300-1400°C and 55-55 kbar. Hydrogen provided local reduction of the samples with separation of metallic iron, which catalyzed the transformation of graphite into diamond. Iron reacted with other elements and was not found in free state in the products of the experiments. Such experiments can be regarded as a simplified model of the formation of some types of natural diamonds during the interaction of reduced fluids with carbon-bearing mantle rocks.