Geological samples from the Nevada Test Site are being analyzed for mineral composition by a rapid, routine X-ray powder diffraction procedure based on the external-standard intensity ratio method. The automated procedure uses X-ray diffraction to analyze each sample for the 12 minerals commonly found at the Nevada Test Site—quartz, montmorillonite, illite, clinoptilolite, cristobalite, feldspars, calcite, dolomite, hornblende, kaolinite, muscovite, biotite, and volcanic glass. The amount (wt.%) of a given mineral component present in the sample is determined by the ratio of the highest integrated intensity peak for the mineral to the highest integrated intensity peak for quartz, together with a constant for the mineral obtained from a calibration curve. The technique is accurate to ±7.0 wt.% of the total sample. The minimum amount of each of these minerals detectable by XRD has been determined, thus placing lower limits on the technique.