Multipole moments play an important role in the application of Mössbauer spectroscopy to study of matter structure. Such a parameter as quadrupole splitting describes the interaction of the nucleus quadrupole moment with the electric field gradient created by other charges of the crystal. Thus, knowledge of the magnitude of the quadrupole splitting makes it possible to identify an unknown substance under study, to make conclusions about its structure, to investigate the local microenvironment of the Fe-57 nuclei in it, and so on.