Supercritical water (scw) is being tested for commercial use in several organic extraction systems, but little work has been done on the extraction of metals from minerals. This lack of information prompted U.S. Bureau of Mines research into the scw treatment of minerals. As a result, this research project is intended to serve mainly as a starting point for further experimentation. A simple flowthrough reactor was built out of high-pressure tubing and used to treat minerals with scw at 400 deg. C and 3,500 to 7,000 psi. The research produced four main conclusions: (1) carbonates of copper, iron, and lead convert to oxides; (2) most iron minerals showed alteration to oxides with some iron dissolution; (3) valuable trace elements including nickel, chromium, and others leached to some extent from sea minerals along with some calcium, iron, silicon, and sulfur; and (4) treatment of sulfides extracted elemental sulfur and resulted in several alteration reactions, though with the exception of cinnabar and the iron-bearing minerals, the metals in sulfides were mainly insoluble. Surface alterations on many of the minerals show significant changes have occurred in the minerals even when only minor extractions were detected. These surface effects may be very important when used in conjunction with flotation processess since the scw treatment may selectively enhance or suppress a mineral's floatability.