The electron microprobe can be used to make accurate determinations of the chemical composition of a very small (1 micron) spot on a sample surface. Quantitative analysis is accomplished by comparing the number of characteristic X-rays for a given element generated by an unknown sample with the number generated by a standard of known composition. An average geochemical analysis takes between 2 and 10 minutes to complete.
This is an example of a quantitative analysis of a plagioclase feldspar. The analysis is recalculated in terms of oxide weight percent (first column) and also in terms of cations for 8 oxygen atoms.
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