Uranium and rare-earth minerals are common accessory minerals in pegmatite deposits. No domestic pegmatites have been found that are rich enough to support an economic mining operation for uranium alone; however, small quantities of uranium minerals may be recovered as by-products of feldspar or mica mining. Madagascar is the only country that has produced appreciable tonnages of uranium minerals from pegmatites.A review of the literature and observations in the domestic pegmatite districts show that the uranium and rare earth minerals generally occur in pegmatites or pegmatite units rich in potash feldspar. Recent mineralogical and structural studies of pegmatites by the U. S. Geological Survey indicate that, on the basis of geologic mapping, these units can be projected laterally and in depth with reasonable accuracy. In most places the mineral content of these units can be estimated with sufficient accuracy for development purposes.