In silicate glasses and melts, water acts according to two main processes. First it can be dissolved in high temperature/high pressure melts. Second, it constitutes a weathering agent onto the glass surface. A number of in-situ x-ray absorption fine structure (XAFS) studies for Fe, Ni, Zr, Th and U show that the more charged cations (Zr, Nb, Mo, Ta, Sn, Th and U) are little affected by the presence of dissolved water in the melt. In contrast, divalent iron and nickel are highly sensitive to the presence of water, which enhance nucleation processes, for example, of phyllosilicates at the A-scale. Such information provides additional constrains on the role of water deep in the earth, particularly in magmatology. By contrast, the weathering of glass surfaces by water can be studied from a durability perspective.
