The index of refraction of an isometric mineral is not the same for all wavelengths of light. When a ray of white light travels from air into a triangular glass prism, the light not only bends but it also is separated into its component colors or wavelengths, the colors of the spectrum. The violet light is bent slightly more than the red, for instance, because it travels more slowly through the glass. As the light emerges from the prism the colors separate even more. This phenomenon, called dispersion, can be observed in some minerals such as diamond. Jewelers refer to this characteristic in gemstones as fire. The next time you look at a diamond, observe the rainbow of colors caused by the splitting of white light into its component wavelengths.