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The results of electron probe microanalysis of several rock-forming minerals by wavelength-dispersive spectrometry (WDS) and energy-dispersive spectrometry (EDS) are compared, and the metrological characteristics of both methods are studied. The measurements were made with the use of a JXA-8100 (JEOL) microanalyzer with five wavelength-dispersive spectrometers and a MIRA 3 LMU (Tescan) scanning electron microscope equipped with an INCA Energy 450 XMax 80 (Oxford Instruments) microanalysis system. Specimens with olivine, garnet, pyroxene, ilmenite, and Cr-spinel grains were analyzed. The variation coefficients that characterize the repeatability of a single determination are found to be ~ 0.5% for WDS and ~ 0.9% for EDS in the compositional range of the main components (C > 10%). For minor components (1% < C < 10%), the variation coefficients are 1.4% and 3.0%, respectively, and for impurities (0.3% < C < 1%), 2.7% and 13%, respectively. For lower contents EDS is almost inapplicable. The ratio of the results obtained by the two methods is reproduced with high precision: For major components, the variation coefficient is 0.56%; for minor components, 1.7%; and even for impurities, it is ~ 8%. The magnitude of the bias is between 0.2 and 3.2 rel.%, which is acceptable. The results show that the accuracies of WDS and EDS are similar for measuring major and minor components of rock-forming minerals. Energy-dispersive spectrometry is inferior to wavelength-dispersive spectrometry for impurities and is completely inapplicable for still lower contents. This method is easier to implement, and the results are available soon after switching on the instrument. Wavelength-dispersive spectrometry needs more time for preparation, but it ensures a precise high-efficiency large-scale analysis of samples of similar compositions, even when the element contents are lower than 1%.

The protocol for analysis of rock-forming mineral compositions by X-ray electron probe microanalysis used at the Institute of Geology and Mineralogy, Novosibirsk, Russia, is described. The analysis is conducted with a JXA-8100 electron probe microanalyzer capable to support a highly stable beam at relatively high probe currents for a long time. Elements that can be assayed range from sodium (atomic number Z = 11) to zinc (Z = 30). The operation conditions for routine analyses are substantiated: accelerating voltage 20 kV, probe current 50–100 nA, and signal accumulation time 10 s at both the peak and the background. The method of analytical problem formulation for measurements is presented. It is proven that the proprietary software is insufficient with the presence of the binary matrix effect and better correction methods are required. Metrological characteristics of the protocol have been studied. The variation coefficient, describing the reproducibility of results, averages 0.9% for major components (C > 10%), 2.5% for minor components (1 < C < 10%), and 6.8% for accessory components (0.3 < C < 1%). With still lower contents (0.05 < C < 0.3 %), the standard deviation of reproducibility is 0.02%. The values of the variation coefficient and standard deviation for measurement repeatability are approximately two times lower. The relative trueness of the method is within 1%. The detection limit (3σ criterion) is generally within 0.01–0.03%. It can be improved by an order of magnitude by increasing the accumulation time and probe current.

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