Book Review: Infrared and Raman Spectroscopies of Clay Minerals

More than 40 years from its publication, The Infrared Spectra of Minerals edited by Victor Colin Farmer (Mineralogical Society Monograph 4, London, 539 pp., 1974) is still a popular reference book for infrared (IR) studies aiming to identify mineral species and to derive information concerning their structure, composition, and reactions in the environment. While most of Farmer’s works are a benchmark in the field of clay and soil sciences, Infrared and Raman Spectroscopies of Clay Minerals aims to update the state-of-the-art in IR and Raman methods applied to the study of clay minerals. Infrared and Raman Spectroscopies of Clay Minerals contains 14 chapters with figures in black and white. Although each chapter in this book is written by several contributors, the authors follow a similar outline and writing style, with each topic clearly introduced and well-articulated throughout. The chapters are also arranged to provide references to the other chapters in which specific topics are overlapped or covered in more detail. However, each chapter may also be read entirely independently from the others. A complete list of references is provided at the end of the book allowing readers to seek further reading material on specific applications of vibrational spectroscopies to clay minerals, accompanied by a useful alphabetical index of topics. Infrared and Raman Spectroscopies of Clay Minerals is conceived to be a continuity of Farmer’s book, credit to Farmer’s career and his scientific contributions is given in the general introduction (Chapter 1). The next three chapters provide a comprehensive overview on the theoretical basis of IR and Raman spectroscopy written for those with a background in solid-state physics (Chapter 2), the advancement of vibrational spectroscopy instrumentation and guidance on the most suitable sampling methods for collecting high-quality spectra (Chapter 3), and the description of spectral processing (Chapter 4). The information presented in these chapters is clear and well-illustrated. The in-depth discussion on the advantages and limitations in modern IR and Raman techniques applied to clay studies is particularly significant. Specifically, the progress achieved in instrumentation [i.e., the advent of fiber optic probes, highresolution detectors, and portable Fourier transform infrared (FTIR) spectrometers] are clearly outlined. The discussion of practical aspects related to the most suitable methods of sample preparation (Chapter 3) and different data manipulation approaches (Chapter 4) to obtain straightforward information from IR and Raman spectra are particularly eye-catching. Given the structural complexities of clay minerals (i.e., site occupancy, isomorphic substitution, order-disorder, structural water, exchanged cations, interstratification, etc.), these chapters are a fundamental learning tool for researchers and professionals. The following chapters offer extensive overviews and exhaustive interpretations of characteristic vibration bands in IR spectra as diagnostic for natural and synthetic clay minerals. Chapters 5, 7, 8, and 9 are a valuable resource for the correct assignment of IR bands, offering scientists an unprecedented capability to study the clay mineral family. The meticulous review and interpretation of IR spectral changes of hydroxyl (OH) groups (i.e., frequency shifts, band intensity and width) in Chapter 5 is of special interest in the attempt to unambiguously identify structural features of a specific clay mineral and explain dehydration and dehydroxylation processes or cation exchange properties. Smectites are the most widely studied of the 2:1 clay minerals. The interpretation of IR spectra is particularly challenging due to the octahedral occupancy and cations relation to their nearest neighbors through shared OH bonds. The discussion on the effects on the OH IR band shifts owing to the crystal chemistry of smectites is given in Chapter 5 and it continues in Chapter 7. American Mineralogist, Volume 104, pages 162–163, 2019