Comprehensive and accurate data on the relative and absolute abundances of the elements are critical to a better understanding of the principles governing their crustal distribution and migration processes. Many geochemically coherent pairs or groups of elements (e.g., the halogens and the rare earths) are difficult to determine chemically. Microanalytical methods combining chemical and x-ray fluorescence techniques have been developed not only to determine these elements rapidly and accurately, but also to provide total analyses of milligram quantities of rare geologic specimens. One of these methods (solution-dilution) is virtually free of matrix effects and is adaptable to the analysis of trace or major constituents. These methods have proven invaluable in the microdetermination of Sc, Y, and the individual rare-earth elements in minerals or rare-earth separates on as little as 1 mg of total sample. Other applications have been the determination of iron in silicates, bromine and iodine in well waters, and the total analysis of small amounts of chromium, sulfide, and carbonate minerals.
Frank Cuttitta and Harry J. Rose, "Micro X-Ray Fluorescence Spectroscopy: Selected Geochemical Applications," Appl. Spectrosc. 22, 423-426 (1968)