This report discusses factors influencing trace element distribution in rocks, tabulates maximum and minimum concentrations of twenty-nine trace elements in various common rock types, and briefly describes the geochemical behavior of each of these elements. A procedure is outlined for predicting concentrations of these selected elements in various rock types. On the basis of this study it is concluded that: 1. Trace element concentration varies systematically according to the gross mineralogical composition of the host rock. 2. Mineralogical composition of the host rock is the primary determinant of trace element concentrations. 3. Knowledge of rock mineralogy as provided by conventional petrographic analyses serves as a basis for estimating trace element concentrations.