Abstract Although absorption of X-rays by matter has been observed since a long time, it is the recent availability of synchrotron radiation sources that has established EXAFS spectroscopy as an important structural tool in geosciences. Nowadays, X-ray Absorption Fine Structure (XAFS, including both the EXAFS and XANES domains) has proven to be an unquestionably useful and powerful method to obtain information on the local and medium-range structural order around a chemical element in condensed matter (solids, liquids, interfaces etc. ). This chapter provides basic information on EXAFS (Extended X-ray Absorption Fine Structure), including some recent experimental developments, both on data acquisition and on spectra reduction, and will be illustrated using recent applications in mineralogy, geochemistry, materials science and environmental science. XANES is separately discussed by Mottana (2004) in this volume. The experimental and theoretical details of extended X-ray absorption fine structure, EXAFS, have been extensively described in the literature ( e.g. Teo, 1986 ; Sayers & Bunker, 1987 ; Koningsberger & Prins, 1988 ; Lytle, 1989 ; Mustre de Leon et al. , 1991 ; Lytle, 1999 ). Recently, the technique has gained wide popularity, due to major breakthroughs both in EXAFS theory and data analysis with (i) the availability of convenient software packages (www.esrf.fr/computing/scientific/exafs/links.html) and (ii) the development of the use of the ab initio multiple scattering code FEFF ( Rehr & Albers, 1990 ; Zabinsky et al. , 1995 ; Ankudinov et al. , 1998 ; Ankudinov & Rehr, 2003 ).

Abstract X-ray absorption spectroscopy has become a common technique in mineral studies only in fairly recent times. It is an element-specific method which is suited to extend structure determination down to the local environment of an atom, i.e. a volume some three orders of magnitude less than that inspected by methods based on X-ray diffraction. However, in line with many other modern techniques, X-ray absorption spectroscopy is neither simple as for the practical operations by which one records high-quality experimental results, nor it is straightforward in the interpretation of them, the more so as minerals are far more complex multi-atomic systems than most compounds investigated by other material scientists. Consequently the mineralogical literature related to X-ray absorption spectroscopy is full of misunderstandings, which may even become traps for a new user. A further motive for the poor interpretation of experimental results that are otherwise technically excellent arises from the bare fact that the theoretical framework of X-ray absorption spectroscopy lies well beyond the basic physics normally taught to mineral and material science students. Indeed, this is possibly why quite a few people have used this powerful technique as if it were a black box (e.g. the ominous “fingerprinting” practice!), or they have overextended the interpretation of spectra beyond what is their true potential content ( cf . Stern, 2001 ). In this chapter, I try to show all what is possible as well as all what is reasonable to obtain by the main absorption spectroscopy methods in use at the present time