This U. S. Geological Survey professional paper discusses aspects of the geology of titanium as a framework for appraising resources of this commodity in the light of today's technology, economics, and geologic knowledge. Contents: Titanium Contents and Titanium Partitioning in Rocks by E. R. Force Metamorphic Source Rocks of Titanium Placer Deposits - A Geochemical Cycle by E. R. Force Rutile and Sphene in Blueschist and Related High-Pressure-Facies Rocks by M. C. Blake, Jr. and Benjamin A. Morgan Titanium Deposits in Anorthosite Massifs by Norman Herz Titanium Deposits in Alkalic Igneous Rocks by Norman Herz Titanium Minerals in Deposits of Other Minerals By E. R. Force