Rhyolite from the "Yellow Stone of Nevsehir" and gamma-irradiated trona from the Ankara Mine have been investigated by electron paramagnetic resonance at ambient temperature and at 113 K. Rhyolite was examined by X-ray powder diffraction and found to consist mainly of SiO2. Before gamma-irradiation, the existing paramagnetic species in rhyolite were identified as PO42-, CH2OH, CO3-, SO2-, CO33-, and CO2- free radicals and Fe3+ at ambient temperature. At 113 K SO2-, CO33- and CO2- radicals and Fe3+ were observed. The gamma-irradiation produced neither new species nor detectable effects on these free radicals. The disappearance of some of the radicals at 113 K is attributed to the freezing of their motions. Before gamma-irradiation, the trona mineral shows only Mn2+ lines, but after gamma-irradiation it indicated the inducement of CO33- and CO2- radicals at ambient temperature, 113 K, in addition to the Mn2+ lines. The g and a values of the species were determined.