Three infrared absorption bands related to fluoride occluded within double four-member ring units of zeolitesexist: one corresponds to fluoride itself and the other two are localized vibrations of the cage appearing ata different wavenumber depending on the presence or absence of fluoride within the cage. This is demonstratedby comparison of the vibrational spectra of a series of as-made and calcined octadecasil materials containingvarying degrees of fluoride and aluminum and is further supported by ab initio quantum chemical calculations.