Three methods of sample preparation of rock specimens have been evaluated for precision and accuracy. A fusion technique was found to give the best precision. Standard deviations (1 σ) using this method and expressed as percent of the amount present for several elements are: Al 0.83, Si 0.64, K 0.43, Ca 0.43, Mn 0.48, Fe 0.24. Three recent studies of compositional variation were performed on volcanic rocks. Analyses of samples from the Hopi Buttes, Arizona, on obsidian flows from Newberry Caldera, Oregon, and on igneous rocks collected from grids or linear traverses give data which, in each case, are useful in making significant interpretations about the geologic history of the rocks concerned. These examples illustrate the rapidity and high quality of quantitative chemical analyses which can be obtained by application of x-ray fluorescence analytical techniques.
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