SYNTHESIS OF CUBIC DIAMOND IN THE GRAPHITE-MAGNESIUM CARBONATE AND GRAPHITE-K2MG(CO3)(2) SYSTEMS AT HIGH-PRESSURE OF 9-10 GPA REGION

Cubic diamond was synthesized with two systems, (1) graphite with pure magnesium carbonate (magnesite) and (2) graphite with mixed potassium and magnesium carbonate at pressures and temperatures above 9.5 GPa, 1600 degrees C and 9 GPa, 1650 degrees C, respectively. At these condi tions (1) the pure magnesite is solid, whereas (2) the mixed carbonate exists as a melt. In this pressure range, graphite seems to be partia lly transformed into hexagonal diamond. Measured carbon isotope delta( 13)C values for all the materials suggest that the origin of the carbo n source to form cubic diamond was the initial graphite powder, and no t the carbonates.