In EPMA analysis of plagioclase in common igneous rocks, measured Fe content can be overestimated by 15-50 percent due to the effect of secondary fluorescence in Fe-bearing adjoining phase such as tholeiitic glass and fayalite, when distance between the analyzed point in plagioclase and adjoining phase is less than 40#mu#m. The present study reports empirical correction equation for measurements of Fe content in the plagioclase based on new experimental data. The magnitude of the over-estimation of Fe in plagioclase is larger than that of Ca in olivine. It is necessary to analyze carefully with respect to the chemical composition of adjoining phases and distance from the interface for quantitative measurements of Fe in plagioclase and Ca in olivine.
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