Home – Home – Jornals – Russian Geology and Geophysics 2002 number 10

Diamond crystallization and character of phase formation in the systems K ₂CO₃-C, K₂CO₃-SiO₂-C, and K₂CO₃-Mg₂SiO₄-C were studied at 6.3 GPa, 1650 °C for 40 h using the multianvil split-sphere equipment. The SiO₂/K₂CO₃ and Mg₂SiO₄/K₂CO₃ ratios were chosen as variable parameters. The degree of graphite-to-diamond transformation and rate of diamond growth on seeds have been determined as a function of these ratios. Composition domains have been revealed in which spontaneous diamond nucleation and diamond growth on seeds proceed. As the concentrations of silica and forsterite in the systems K₂CO₃-SiO₂-C and K₂CO₃-Mg₂SiO₄-C, respectively, increase to 10 wt.%, the diamond formation becomes more intense. Given a further increase in contents of SiO₂ or Mg₂SiO₄, this intensity gradually decreases until the complete termination of spontaneous nucleation and then, diamond growth on seeds. The conditions were created under which diamond was crystallized from a potassium carbonate-silicate melt, including the main components of deep-seated ultra-potassium fluxes, together with coesite in the system K₂CO₃-SiO₂-C and with forsterite in the system K₂CO₃-Mg₂SiO₄-C.