Quantitative determination of dawsonite in Green River Shale by powder-sample X-ray diffraction; effect of grinding

In an effort to evaluate the method of quantitative analysis by X-ray diffraction as a means of determining dawsonite abundances in Green River" oil shale, we performed a series of grinding experiments. Weighed mixtures of dawsonite + quartz and dawsonite + quartz + shale were ground for preset lengths of time, and the following X-ray diffraction peaks were measured for intensity: dawsonite (110) at 15.6 2θ and (211) (002) at 32.1° 2θ, and quartz (100) at 20.9° 2θ and (101) at 26.6° 2θ. Heights and areas were measured. Intensity ratios were plotted as functions of grinding time with a calculated probable error. Intensity ratios generally decrease as grinding time increases. The intensity of the 15.6° peak, D_15.6°, is most affected, and the most drastic reduction occurs during the first 20 min of grinding. The D_32.1° peak is least sensitive to grinding but is subject to interference by other minerals in the shale. We conclude that the X-ray diffraction method is not well adapted to the routine quantitative determination of dawsonite in oil shale of the Green River Formation.