To assess the effect of pressure on the coordination state of Fe3+, experiments have been conducted on silicate melts in the NA2Fe2O3-SiO2 system in the presence of O2 to pressures of 4 GPa and temperatures of 1700¿C. Quenched melts (glasses) have been analyzed using 57Fe M¿ssbauer spectroscopy at 298K. Fe2+ was not detected in any glasses and the absorpiton in the M¿ssbauer spectra, consisting of two peaks, is entirely from Fe3+. Two peaks in the spectrum are symmetric at low pressure and are attributed to Fe3+(IV). The isomer shift of the Fe3+ doublet increases ~0.10 mm/s form 1 bar to 4 GPa. Above 1.5 GPa in iron-rich compositions, the spectra become asymmetric with the low-velocity peak becoming less intense and broader suggesting the presence of a second component. This component can be either a result of increasing distortion of Fe3+(IV) or a result of the gradual coordination change of Fe3+ from IV to VI. This coordination change for Fe3+ has been previously observed in glasses in the NA2O-SIO2FE-O at high pressure and lower values of f02 as the Fe3+ is partially reduced to Fe2+. The effects of pressure on the coordination state of Fe3+ and the Fe3+&Sgr;Fe affect the compressibility of a magma at depth. It is anticipated that the presence of Fe3+(IV) at high pressure will favor a higher compressibility than if Fe3+ transforms to Fe3+(VI) or if the Fe3+ is reduced to Fe2+. ¿American Geophysical Union 1990