X ray Compton scattering is a potential procedure for investigating crystal defects. Its application to a belite sample doped with 1% K or Co revealed the considerable effects of slight impurities on the fine structure of Compton scattering profiles, which were otherwise undetected by conventional methods. Impurities generate interatomic bonds attenuation which, in turn, generate additional intense and narrower lines on the fine structure, different for every impurity.