The effect of silica on ferric/ferrous ratio in silicate melts: An experimental study using Mossbauer spectroscopy

We conducted a Mossbauer study of synthetic glasses with anorthite-diopside eutectic composition modified with either 5 or 1 wt% Fe2O3 and variable amounts of silica. Glasses were synthesized in air in the temperature range 1400-1570 degrees C. Room-temperature Mossbauer spectra showed the presence of magnetically ordered Fe3+, for which a systematic fitting procedure was developed to correctly estimate Fe3+/Fe2+. At constant T-fo(2) we observed a minimum in the variation of Fe3+/Fe2+ ratio with silica that varied from 56 to 63 wt% SiO2, depending on temperature. It was also demonstrated that the temperature dependence of the ferric/ferrous ratio [log(Fe3+/Fe2+) vs. I/T] is essentially similar for basic and silicic melts.