9725047 Yund Fine-grained samples consisting of forsterite and plagioclase saturated with impurities such as Rb, Sr and Ba will be hot-pressed. These polycrystalline samples will be annealed at T and P (and quenched) in order to establish equilibrium between grain boundary region and the bulk crystal. Compositional differences between the grain boundary region and adjacent regions of the bulk crystal will be determined using SEM. Differences in concentrations of solutes equivalent to a tenth of a monolayer on a grain boundary can be determined. Grain boundary diffusion experiments will be made on the above aggregates. Stable isotope traces will be used at a variety of T and P and concentration profiles will be determined via ion probe.
