The Infrared Spectra of Minerals
The principal concern of this book is the use of vibrational spectroscopy as a tool in identifying mineral species and in deriving information concerning the structure, composition and reactions of minerals and mineral products. This does not mean that the approach is purely empirical; some theoretical understanding of the vibrational spectra of solids is essential to an assessment of the significance of the variations in the spectra that can be found within what is nominally a single mineral species, but which usually includes a range of compositions and defect structures. Theory alone, however, can give only limited support to the mineral spectroscopist, and careful studies of well-characterized families of natural and synthetic minerals have played an essential role in giving concrete structural significance to spectral features. The publication of this book represents a belief that theory and practice have now reached a state of maturitity and of mutual support which justifies a more widespread application of vibrational spectroscopy to the study of minerals and inorganic materials. The wide area of theory and practice that deserves to be covered has required a careful selection of the subject matter to be incorporated in this book. Since elementary vibrational spectroscopy is now regularly included in basic chemistry courses, and since so many books cover the theory and practice of molecular spectroscopy, it has been decided to assume the very basic level of knowledge which will be found, for example, in the elementary introduction of Cross and Jones (1969). With this assumption, it has been possible to concentrate on those aspects that are peculiar to or of particular significance for mineral spectroscopy.
The vibrational properties of any solid, no matter what its internal structure, are associated with much of its observable macroscopic behaviour. Thus it would seem obvious to say that a study of vibrational spectroscopy must be extremely important for a better understanding of the nature of the solid state.
The range of vibrational frequencies is very wide and a knowledge of the distribution of frequencies is a fundamental requirement in the calculation of many thermal properties, for example. More than this is possible, however, if changes in dipole moment or polarizability occur during the vibrational movements, since in principle the infrared and Raman spectra of the system can then be calculated. This interrelationship between the density of states, the IR spectrum and the Raman spectrum is only now becoming established and much of the previous study of IR or Raman spectra was concerned with identifying the dominant stretching or bending “modes” which gave rise to the observed bands. There is no doubt that many important results have been discovered by means of this indirect approach and an enormous amount of data has been accumulated. It is the purpose of this review article to guide the reader to those papers in the literature which the author feels have been important in the development of the subject to the position it holds today. No attempt has therefore been made to include all aspects of the IR and Raman spectroscopy of glasses, but some of what is omitted may be found in other