  For polycrystalline specimens of zeolites treated to thermal oxidation we
have revealed and studied the weak spectra of reproducible magnetic microwave
absorption fluctuations at a frequency of 9.4 GHz. The investigation was
carried out by the ESR method over the 77-500 K temperature range. The
fluctuation spectra have features typical of mesoscopic phenomena observed
previously in ESR spectra of high temperature superconductors and metals at
temperatures below critical. The similar fluctuation spectra were obtained at
300 K for some oxides, oxidized silver and gold particles. The experiments
performed are, perhaps, the first observation of the phenomenon at unusually
high temperatures which has been observed only in superconducting systems.
