Natural and synthetic gem rubies can be separated on the basis of their trace-element chemistry as determined by energy-dispersive X-ray fluorescence (EDXRF) spectrometry. This method is especially important for rubies that do not have diagnostic inclusions or growth features, since such stones are difficult to identify using traditional gem testing methods. The results of this study indicate that the presence of nickel, molybdenum, lanthanum, tungsten, platinum, lead, or bismuth proves synthetic origin, but these elements were not detectable in most of the synthetic rubies tested. Alternatively, the concentrations of titanium, vanadium, iron, and gallium––considered together, as a trace-element “signature”––provide a means for separating nearly all synthetic from natural rubies. EDXRF can also help identify the geologic environment in which a ruby formed, and thus imply a geographic origin.