9418437 Giletti A principal goal of this research is to understand the mechanisms and controlling parameters that govern diffusion in minerals, particularly by cations. The focus will continue to be the feldspars, in order to develop a systematic and sufficiently comprehensive body of data. These data will form the basis for a predictive model for cations, including those not studied. The proposed research will include determining the diffusion mechanisms and their controlling factors for cations in feldspars, developing a theoretical basis for predicting diffusion kinetics behavior, continuing to measure the Pb diffusion in monazite and extend it to other minerals such as titanite and rutile, and extending determination of Sr diffusion kinetics to mica, apatite and titanite. The two latter studies are especially important in defining precisely the diffusion behavior of geochronologically important systems so that realistic interpretations of th edata can be made. Most of the analytical data will be determined by ion microprobe.