Abstract Redox-reactive minerals can serve as electron donors or acceptors for abiotic reactants or microbial metabolic processes, and hence can play important roles in terrestrial and aquatic environments, particularly if their reaction rates are comparable to those of other biogeochemical processes. Under such circumstances, their reactions can control metal and contaminant bioavailability and change the permeability of soils and sediments. While the thermodynamic driving force for a mineral redox reaction is frequently a good predictor of relative rates of reaction, there are many examples in which kinetic factors limit reaction rate. Understanding the thermodynamic and kinetic aspects of mineral reaction rates, and their sensitivity to environmental conditions such as temperature or pH, is important for anticipating the biogeochemical evolution of natural environments subjected to change. Achieving this goal requires knowledge of the reaction pathway, the timescales of intermediate steps, and the lifetimes of metastable reaction states. Mineral redox reactions proceed through a combination of steps that can include electron and proton transfer, the breaking or formation of bonds, and mineral dissolution or phase transformation. The combination of conventional kinetics approaches, newly-developed ultrafast time-resolved methods and molecular simulation can provide elucidation of such complex reaction pathways. This chapter summarizes key concepts in mineral and interfacial redox reactions with illustrations from the rich geochemistry of iron and iron-bearing minerals.

Abstract A continuous spectrum of photon radiation is produced when accelerated charged particles are deflected by electric or magnetic fields. For electron storage rings this radiation is produced by path bending magnets or insertion devices, and is called synchrotron radiation. It commonly spans energies from the far infrared to hard X-ray regions, has extremely small beam divergence and is orders of magnitude brighter than photons from X-ray tubes. The radiation is also strongly polarized in the plane of the storage ring, and has a pulsed structure in time, allowing for experiments that can resolve kinetic phenomena on the order of the pulse separation. Specialized insertion devices augment the radiation available from bending magnets. Wigglers essentially act as the sum of many bending magnets, producing high photon fluxes. Undulators produce interfering radiation fields that result in non-continuous spectral output, but extremely high brightness and high coherency. Other important X-ray optical elements include grazing-incidence mirrors for beam focusing, crystal monochromators for energy selection, zone-plate optical elements for nanoscale beam focusing and phase contrast microscopy, and detector systems for measuring high count rates with highenergy resolution. Present synchrotron facilities allow a number of powerful spectroscopic, diffraction, and imaging techniques to be widely available to a broad user base. Access to such facilities is also described.

Abstract This volume presents the majority of topics in synchrotron science that are of use to the clay science community. The chapters presented in this volume serve not only as significant statements on the state of these applications, but also as useful primers to potential new users of synchrotron facilities.