This invention relates to a method and system for determining the composition of an unknown sample. The present invention is directed to a method of calibrating an x-ray spectrometer that does not require measuring all possible elements under the operating conditions used to measure the unknown sample to be analyzed. According to a preferred embodiment, the local instrument can be calibrated from an x-ray spectrum of a single elemental standard. The instrument will have a stored library containing high quality spectra for all elements being analyzed. The analysis of the single element is compared to the library spectra for that element to define a transformation that is used to create a calibrated spectra library that includes a calibrated spectrum for each spectrum in the original library. The spectra generated by the local instrument can be compared to the calibrated library spectra to determine the elements in an unknown mineral.