X-ray fluorescence determination of the FeO/Fe2O 3 tot ratio in rocks

Chances for estimating the FeO/Fe2O (3) (tot) ratio in rocks by the K and L series of X-ray fluorescence spectra are studied. The errors in the determination of FeO/Fe2O (3) (tot) by the intensity ratio of the K beta(2,5)/K beta(1,3) and L beta/L alpha(1,2) lines are compared. The relative standard deviation of determining FeO using a set of 49 standard samples of eruptive rocks varies in the range 5-16%, depending on the ratio FeO/Fe2O (3) (tot) and the concentration of FeO. The better precision is attainable for a ratio above 0.45 at a FeO concentration in the range 5-15%. For samples of andesites and basalts, the relative standard deviation is better than 4%, for rocks of the granite family it is 23% at FeO concentrations below 3%. For samples of metamorphic and sedimentary rocks, the error of FeO determination is higher than that for the eruptive ones. For samples with the ratio FeO/Fe/Fe2O (3) (tot) < 0.25, the deviation may exceed 30 rel %. In contrast to chemical analysis, the X-ray fluorescence method appears advantageous in time and cost of sample preparation and can be used for routine analysis in geochemical research.