Contributions to Industrial-Minerals Research, a biennial series of U.S. Geological Survey (USGS) Bulletin chapters, presents research strategies, results, and updates of investigations of industrial minerals by USGS scientists and cooperators. Industrial minerals are defined as valuable nonmetallic, nonfuel geologic materials, generally rocks or minerals, used in a wide range of construction and industrial applications—for example, sand, gravel, and crushed rock used as aggregate for construction; limestone used for cement; phosphate for fertilizers and insecticides; and diatomite used for filtration, fillers, and abrasives. The term also comprises some processed materials, such as cement and metallic compounds with major utilization in nonmetallic forms. For example, titanium is commonly grouped with industrial minerals because more than 90 percent of it is sold and utilized in the form of the oxide (TiO₂) rather than as Ti metal. Other metals and metallic compounds commonly grouped with industrial minerals include Mn, Cr, Fe oxides, and rare-earth elements (REEs).