Abstract: A rock specimen is step scanned in an electron probe x-ray microanalyzer. A plurality of x-ray spectrometers (for example three) forming a part of said electron probe x-ray microanalyzer simultaneously detect characteristic x-rays corresponding to three elements at each scanning point on the rock specimen. The concentration of each element is calculated from the output signals of said plurality of x-ray spectrometers and the calculated elemental concentrations are then converted into atomic ratios accordingly. From this information, the type of mineral at each scanning point is designated by a character which is recorded on a display means in synchronism with the step scanning so as to display a mineral map of the specimen being examined.