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Fe2+is the most abundant iron species in magmas and in many slags. Its structural role in these liquids is poorly understood, largely because of the difficulty of studying melts at high temperatures by direct structural methods. Whether Fe2+behaves as a network modifier, network former or free-ion complex has not been adequately resolved, yet this is fundamental to understanding the properties of silicate liquids. Also uncharacterized are the structural changes accompanying the melt-to-glass transition in Fe-bearing silicate melts. Here we report the results of a high-temperature synchrotron-based X-ray absorption study of Fe in silicate glasses and melts of compositions near Na2FeSi3O8and K2FeSi3O8. The glasses were also analysed by 57Fe Mossbauer spectroscopy. We conclude that Fe2+is a four-coordinated network former in these melt/glass systems and that little structural relaxation occurs at the iron site during the melt-to-glass transition. These results and structural data for Fe22+SiO4melts1suggest the possibility of a pressure-induced change from four- to six-coordination for Fe2+in magmas in the Earth's upper mantle.