[en] We present studies of phase dynamics of the silicon rich part of the Fe-Si system performed with Moessbauer spectroscopy. Standard spectra are obtained in very pure samples and these are applied to the studies of commercial 75% ferrosilicon. We find that the semistable high temperature alpha phases, known for considerable concentration of vacancies, needs multiple quadrupole doublets to fit the data. Finally it is shown how the Moessbauer effect can be applied to quality control in ferrosilicon production. (orig.)