Raman spectra have been measured in the spectral range from 1000 to 1800 cm(-1) on samples of amorphous carbon modified with platinum in amounts comparable with that of carbon. Also, Rutherford backscattering spectra have been studied. It is shown that, as the platinum concentration is raised to similar to 0.5 x 10(22) at cm(-3), the average size of graphene clusters increases. As the platinum concentration increases further, the graphene clusters become smaller in size.