The principal investigators will experimentally and theoretically investigate cation and anion distributions in minerals, primarily using X-ray and neutron diffraction techniques. They also will compile a large computer data base of mineral crystal structure determinations, and in turn use the data base to generate X-ray powder diffraction patterns for the same minerals. The results of these efforts will provide basic data that is of interest to many earth scientists, especially mineralogists and petrologists, as well as to investigators in other disciplinary areas such as materials science.