The synchrotron x-ray fluorescence microprobe at bending magnet beamline X-26A at the National Synchrotron Light Source has been used for a number of years for geochemical trace element microanalysis using collimated white radiation. More recently an incident beam monochromator and 8:1 focusing mirror have been added. These optics permit the formation of a small (30-100 micron) intense beam of monochromatic radiation suitable for use in x-ray absorption spectroscopy, including both near edge (XANES) and extended fine structure (EXAFS) techniques. This system has been used to study a number of problems in the earth and environmental sciences, including: oxidation state of uranium in contaminated waste sites; oxidation state of Cr in olivine inclusions in diamonds from the Earth's mantle; oxidation state of Mn in wheat roots infected with the take-all disease. We report here some recent results obtained on studies of the oxidation state of Fe in cosmochemical systems.Oxygen fugacity is one of the most important parameters in determining the cosmochemical and geochemical evolution of a system.
