Sample preparation and methods of calculation used by the Division of Ohio Geological Survey in its mineralogic and physical characterization of the Upper Devonian black shales are described. Methods of sample mounting, used in conjunction with a Philips automatic sample changer (ASC), allow analysis of a large number of samples by x-ray diffractometry. Because of the time saved wth an ASC, each sample can be scanned twice to increase the precision of the results. The reproducibility of the x-ray data, expressed as relative deviation, ranges from about +-2 to +-10% in samples for which the percent total integrated intensity (%TII) is above 6%.