Abstract The Rietveld method was originally developed (Rietveld, 1967, 1969) to refine crystal structures using neutron powder diffraction data. Since then, the method has been increasingly used with X-ray powder diffraction data, and today it is safe to say that this is the most common application of the method. The method has been applied to numerous natural and synthetic materials, most of which do not usually form crystals large enough for study with single-crystal techniques. It is the ability to study the structures of materials for which sufficiently large single crystals do not exist that makes the method so powerful and popular. It would thus appear that die method is ideal for studying clays and clay minerals. In many cases this is true, but the assumptions implicit in the method and the disordered nature of many clay minerals can limit titsapplicability. This chapter will describe the Rietveld method, emphasizing the assumptions important for the study of disordered materials, and it will outline the potential applications of the method to these minerals. These applications include, in addition to the refinement of crystal structures, quantitative analysis of multicomponent mixtures, analysis of peak broadening, partial structure solution, and refinement of unit-cell parameters.

Abstract Over centuries mineralogy has developed from a mainly descriptive scientific discipline to a quantitative experimental research field covering a wide area. A broad spectrum of different mineralogical disciplines, ranging in their topics from the macroscopic physical and chemical properties of igneous rocks up to the atomic structures and characteristics of minerals, crystals and materials is applied today. Mineralogy can be regarded as a field of both Earth sciences and materials science and is an extraordinarily manifold scientific discipline with numerous points of contact to geology, chemistry, physics and materials science, characterised by the large variety of methods used in basic and applied research. A wide variety of analytical methods such as diffraction methods, microscopy, thermal analysis and spectroscopy is used in the different research fields of mineralogy, each method contributing small pieces to the large puzzle of unsolved scientific questions. Often several methods fail in the investigation of structural aspects as in the case of amorphous materials ( e.g. glasses from magmatic melts) or microcrystalline materials and for specific structural questions, e.g. the location and dynamics of hydrogen atoms in minerals. Solid state nuclear magnetic resonance can be an ideal complementary method here. All nuclei that possess a magnetic moment ( I > 0) are able to provide detailed information about their local environments as local probe, e.g. about bond angles, neighbouring atoms (1 st and 2 nd coordination sphere), local symmetry, the coordination number, as well as being sensitive to dynamic processes ( Chandrakumar & Subramanian, 1987 ; Ernst et al ., 1987 ; Fyfe, 1983 ; Slichter, 1990 ).