taining up to about 26 mol% Fe,O, were studied. Pronounced changes in properties were observed a t compositions containing about 6, 10, and 13 mol% FezO,. The X-ray diffraction spectra of devitrified (heat-treated) samples showed new compounds near these compositions. Electron spin resonance and optical studies confirmed the presence of Fe3+ and Fez+ in both 4 and 6-coordination. An increase in total iron in these samples was associated with a decrease in the ratios Fez+ 4-coordinated/FeZ+ 6-coordinated and Fe'+ 4-coordinated/Fe3+ &coordinated up to about 2.0 mol% Fez03, as shown by the intensity of the optical absorption bands at about 2.0 and 1.0 2 o,5 a respectively. Samples containing up to 4.3 mol% FezO, showed u F 0.4 an increase in Fex+ concentration and a decrease in Fez+ cona 0 0 . 3 centration after gamma irradiation. The electrical conductivity and activation energy decreased sharply with increasing Fe,O, content. 0.9 0.8 0.7 > I-V, 0.6 pm and by the intensity of the ESR lines at ge4.2 and 2.0, -I 0.2