The principal investigator will study the kinetics and mechanism of aqueous oxidation of the minerals pyrrhotite and troilite under a variety of geological conditions. Principal techniques to be employed are Mossbauer spectroscopy and chemical analysis for dissolved ionic iron and sulfur. A variety of surface-sensitive spectroscopic techniques also will be utilized to detect transient species on mineral surfaces and to in turn help determine reaction mechanism. This research will lead to a better understanding by geologists of the rates of formation of seafloor iron ochre deposits from marine sulfide-bearing assemblages and of gossans above ore deposits.