Abstract

Quantitative X-ray diffraction analysis gives data on quartz, feldspar, and carbonate in shales with a precision of + or -10 percent; clay mineral content is determined by difference. Obviously silty and calcareous shales were not included among the 400 samples from Tertiary rocks of the Gulf Coast, Mesozoic rocks from the western interior of the United States and Canada, and Paleozoic rocks from the Marathon Uplift, Big Bend Arch, Ouachita, and Appalachian areas, and 57 samples identified only as miscellaneous. Means (percent) and standard deviations for about 300 of these samples are quartz, 33.6, 15.2; feldspar, 3.6, 4.8; carbonate, 2.7, 8.4, and clay minerals, 64.1, 9.4. The inclusion of an additional 100 unidentified samples changes the means to quartz, 30.8; feldspar, 4.5; clay minerals, 60.9; carbonates, 3.6; iron oxides, >0.5; organic matter, 1; and other minerals, 2 percent.

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