Method for high pressure catalyst-free synthesis of high purity nano- and micronsize diamond powder from hydrocarbonltluorocarbon mixture under heating at 1000 °C at 8 GPa. i.e. under conditions of thermal stability of diamond. has been developed. This method is unique in that (i) using a mixture of hydrocarbons with fluorocarbons as precursors in absence of any catalysts reduces by 300°C the temperature of diamond synthesis as compared to use of just pure hydrocarbon precursors, (ii) produces high yields of well-faceted nanosize (9-100 nm) along with a micronsize (0.3-13 )lm) diamond crystals of high purity, shown by very low ash content (0.l±0.05 wt.%),.