Nanoparticle properties can show marked departures from their bulk analog materials, including large differences in chemical reactivity, molecular and electronic structure, and mechanical behavior. The greatest changes are expected at the smallest sizes, e.g. 10 nanometers and less, where surface effects are likely to dominate bonding, shape, and energy considerations. The precise chemistry at nanoparticle interfaces can have a profound effect on structure, phase transformations, strain, and reactivity. Certain phases may exist only as nanoparticles, requiring transformations in chemistry, stoichiometry, and structure with evolution to larger sizes. In general, mineral nanoparticles have been little studied.