The traditional gemological technique for distinguishing natural from synthetic blue spinel has involved the use of refractive index and absorption spectra. Recently, however, the standard interpretation of these tests has proved troublesome in the identification of several intensely colored blue stones that have refractive indexes in the range of natural blue spinels but that exhibit spectral features generally associated with synthetic cobalt colored spinels. To establish the origin of these specimens, a detailed investigation of natural, flame-fusion, and flux blue spinels was carried out. The results indicate that, while spectral features in the longer wave lengths are unreliable for separating these spinels, an iron related absorption band at about 460 nm was seen only in our natural specimens. Flame-fusion synthetics may still be distinguished by their lower refractive indexes. -- AATA