Experimental study on diamond nucleation and growth in carbon solution in the multicomponent carbonate, carbonate-silicate, silicate and sulphide melts is performed. High-pressure toroidal anvil-with-hole cell with graphite resistive furnace was used. The boundary conditions of diamond spontaneous crystallization and seeded growth are determined for all the diamond growth media with the use of the PT diagram of diamond crystal growth. Raman spectra of quenched carbonate-carbon, carbonate-silicate-carbon, silicate-carbon and sulphide-carbon melts contain bands relating to region of stretching C-C in diamond and graphite microphases.