corundum, color.4, gems

Most gemologists are familiar with the direct vision spectroscope. This instrument uses a series of prisms or a diffraction grating to separate white light into its spectral components. If white light is passed through a gem, it will reveal any areas of absorption or emission. The main limitation of the direct vision spectroscope is that it can only analyze the visible region (400–700 nm), but a small portion of the electromagnetic spectrum.