Analysis was carried out on obsidian from several geological sources in the Pacific Northwest employing tube excitation of a secondary target as a source for photon-excited energy-dispersive x-ray fiuorescence. Results are expressed as average peak intensities normalized to the Zr Kalpha peak at 15. 76 keV plus any unresolved Sr KÊ3 contribution. It was concluded that obsidian fiows can be differentiated on this basis.