Quantitative X-ray powder diflraction (XRD) and X-ray transmission (XRT) procedures have been combined with X-ray fluorescence (XRF) and other spectroscopic methods to characterize the mineralogy and chemistry of 33 core samples obtained from the Salton Sea Scientific Drilling Program (SSSDP) well. Major mineral components in the SSSDP samples include quartz, orthoclase, sodic plagioclase, chlorite, epidote, illite, and calcite, with minor pyrite, phlogopite, halite, anhydrite, and actinolite. Compositions of orthoclase, albite, epidote, and chlorite were determined by microprobe analysis from polished sections of SSSDP core samples for use in the XRD oxide reductions. From these mineral compositions, the weight fractions of the minerals (mineral modes) were computed from bulk chemical analyses obtained by XRF spectrometry using a least-squares minimization procedure. Measured and calculated mass-absorption coefficients were compared to locate errors in analytical parameters or in mineral chemistry. This study demonstrates the value in obtaining good bulk and individual phase chemistry for use in quantitative multicomponent X-ray diffraction analysis.