Absorption spectroscopy of ionic and molecular units in crystals and glasses

All minerals have regions of strong absorption of electromagnetic radiation in the ultraviolet, visible, or infrared portions of the spectrum, which arise from electronic and vibrational transitions of the various ions in the minerals. The study of the ultraviolet spectra of minerals is a comparatively neglected subject because the absorption bands in the ultraviolet are so intense that it is experimentally difficult to prepare samples thin enough to transmit the amount of light necessary for measurements of the spectra. The study of the infrared spectra of minerals is an important and expanding field, and is the topic of several of the following chapters. The region in between, the visible and near-infrared portions of the spectrum, extending from 400 to 2500 nm (0.4-2.5 µm), is the spectral region discussed in this chapter.