Absorption spectrum - The specific bands of light that pass through and those that get absorbed in a gem or mineral and disperse into the colors of the spectrum. Different gems have different absorption spectra, meaning they are all unique in regard to which colors are absorbed and which pass through. This plays a major role in identifying gems, and can easily distinguish between an imitation gem that has properties almost identical to the real thing. A spectroscope is used to determine the absorption spectra of a mineral.