We have developed a systematic procedure to analyze vibrational motions in complex molecules and solids with large unit cells. This procedure, based on group theoretical arguments, has been used to analyze the normal modes of sodalite. We find that certain linear combination of normal modes are : strongly spatially localized on the secondary building units (SBUs) of this zeolite. Further, some of these local motions are combinations of weakly coupled normal modes. This analysis leads us to believe that many of the normal modes can indeed be uniquely associated with the SBUs of sodalite.