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.
The detailed dependence on wavelength of the intensity of radiation absorbed by a given medium. Absorption spectra of gases are typically composed of discrete spectral lines and bands of overlapping lines that depend on the molecular or atomic composition of the absorbing substance and that may be used to identify it uniquely. When measuring the absorption spectrum, the medium should be considerably colder than the source of incident radiation (which should also be continuous in wavelength), in order to clearly distinguish the absorption spectrum from the analogous emission spectrum.
The array of absorption lines and absorption bands that results from the passage of radiant energy from a continuous source through a selectively absorbing medium cooler than the source.