Electronic polarizabilities of cations have been obtained for the sodium D line (in Å 3): Mg2+ 0.1, Fe2+ 3.3, Zn2+ 5.4, Zr4+ 4.6. The polarizability of the O2- ion varies from one structure to another. It has been shown that calculation of electronic polarizability is possible only if an accurate structure refinement is available.