Formation of various types of graphite inclusions in diamond: Experimental data

As a result of experiments on diamond crystallization and annealing, diamond crystals with graphite inclusions were produced. Crystallization of diamond was realized in dry and water-containing chloride, carbonate and silicate systems at P = 5.7–7.5 GPa and T = 1400–1800 °C using high-pressure equipment of “split-sphere” type. Annealing of diamond crystals in the field of thermodynamic stability of graphite was carried out at P = 7.0 GPa and T = 2500 °C, as well as at 1500 °C in vacuum (10− 5 atm). As a result, we produced diamond crystals with graphite inclusions of three genetic types (protogenetic, syngenitic and epigenetic). Initial graphite and newly formed diamond and graphite were studied using optical and scanning electron microscopes, as well as micro-Raman spectroscopy. It was shown experimentally that graphite inclusions in diamond crystals could form not only within the graphite stability field prior or after diamond crystallization, but also within the diamond stability field as a result of joint crystallization of diamond and graphite. The features of graphite inclusions' morphology, Raman spectra, and strain patterns around the inclusions could be indicators of the mechanism of inclusion formation.