Synchrotron‐based X ray absorption studies of cation environments in Earth materials

Since its development in the early 1970s, synchrotron‐based X ray absorption spectroscopy (XAS) has proven to be a versatile structural probe for studying the local environments of cations in a variety of earth materials ranging from crystalline solids, silicate glasses, and high‐temperature silicate melts to aqueous sorption systems which involve metal complexes associated with (or sorbed at) mineral/water interfaces. The structural information provided by XAS includes average interatomic distances and the number and chemical identities of neighbors within 5–6 Å of a selected cation. In many cases (e.g., short‐range ordering of cations in minerals; cation environments in gels, glasses, melts, and metamict (radiation damaged) minerals; and the structure and composition of sorbed species at mineral/water interfaces), XAS provides unique structural data not duplicated by other methods. This paper presents a tutorial review of the physics underlying XAS and data analysis methods and a selective review of applications of XAS to earth materials.