Abstract Intercalation is the inclusion or reversible insertion of a guest chemical species (atom, ion, molecule) in a virtually unchanged host-crystal structure. Any type of layer-structured material may give rise to intercalated compounds, the guest species being artificially inserted or naturally included between the host sheets without loss of their planarity. Layer silicates, in particular, may be considered intercalated structures where interlayer guest species and complexes are inserted between the silicate layers. The most common guest species is H 2 O, which is generally present under natural conditions in intercalated layer silicates such as smectites, vermiculite and halloysite. Past research focused attention on the swelling/shrinking behaviour of intercalated compounds with respect to H 2 O, and also on the non-stoichiometric, heterogeneous complexes formed from organic liquids such as ethylene glycol and glycerol. The unique combination of layer-silicate features (small crystal size, large surface area) and the small concentrations required to effect a change in the matrix, both coupled with the advanced characterization techniques available, have generated much interest. This interest extends to the special field of nanocomposites, and of graphene, which is also an intercalated layered structure. In general, any guest material inserted into an interlayer space causes a modification in the structure, with spacing-size changes in a particular crystallographic direction (d value). First, a brief introduction on conventional and synchroton-based X-ray techniques used to define crystal size and thickness is given. Then, the peak-broadening approach by conventional X-ray diffraction (XRD) techniques, such as the Scherrer method is presented. Further on, the crystallinity measurements and the Bertaut-Warren-Averbach (BWA) method used in the MudMaster program are described. A short summary is presented of the grazing-incidence diffraction (GIXRD) technique. Finally, additional and complementary information from X-ray absorption spectrometry (XAS), such as short-range order, and detailed local information on atomic positions by angle-resolved X-ray absorption near-edge stucture (AXANES), polarized extended X-ray absorption fine structure (P-EXAFS), and near-edge extended absorption fine structure (NEXAFS) spectroscopies are analysed and discussed. Examples of the applications of these methods to clay minerals, micas and graphene are given.

Under the pressure of industrial demands following the discovery of South African diamonds, gemology became a science during the late nineteenth century by combining morphological mineralogy with mineral physics and chemistry. However, it underwent an empirical, pre- to semiscientific period during the Renaissance, when market novelties required development in gemological knowledge. Pliny's Naturalis Historia (1469) was the reference treatise on gemstones among scholars, but it was the Italian translation of this work by Landino in 1476 that made gem studies grow. Indeed, while scholarly mineralogy developed through Latin texts, practical arts related to minerals developed through light handbooks in the new European languages. In Italy, the most active trading center at that time, where luxury goods were brought to be set in gold and distributed to all of Europe, most gem traders possibly understood some Latin, but certainly their providers did not, nor their customers. This is why the first original Renaissance book on gems, Speculum lapidum , by Leonardi (1502) , did not enjoy popularity until it was translated into Italian by Dolce in 1565. Similarly, Barbosa's accounts of travel to gem-producing India (1516) became known only after Ramusio translated them in 1554. Among gemological contributions in Italian, the most farsighted ones are Mattioli's translation of Dioscorides' De materia medica (1544) and Cellini's Dell'oreficeria (1568) . Moreover, three manuscripts did not reach the stage of being printed: Vasolo's Le miracolose virtù delle pietre pretiose (1577) , Costanti's Questo è ‘l libro lapidario (1587) , and del Riccio's Istoria delle pietre (1597) . They survived, however, to help clarify gem interests and activities by the merchant class in the transitional time from the Renaissance to the Baroque. Then, Italy lost its top position in culture and trade, and a Fleming, A.B. de Boot, wrote the treatise that summed up the available knowledge on gems at that time (1609).

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