This pilot project will characterize the Li isotopic composition of the Earth's mantle. This project will concentrate on both solution and laser introduction of Li to our Nu plasma multicollector ICP-MS. We will begin by analysing international rock standards in solution, then will proceed with mineral separates from peridotites (olivine, orthopyroxene and clinopyroxene). Our ultimate goal is to determine the range of Li isotope values in the Earth's mantle, as sampled by a variety of peridotitic xenoliths derived from lithosphere of variable ages and tectonic settings that have experienced a variety of metasomatic overprinting processes. In addition, we hope to establish the degree of isotopic heterogeneity between coexisting phases.