1. A method for classifying a composition of a sample of unknown composition, the method comprising: a. illuminating a portion of the sample with a first beam of penetrating radiation, the first beam characterized by a first pre-specified set of beam settings; b. detecting x-ray emission emanating from the sample; c. performing a complete spectral analysis of the x-ray emission; and d. categorizing the composition of the sample based on the complete spectral analysis, at least with respect to metallic content.