PREVIOUS chapters have surveyed the structures of ordered and disordered clay minerals and related layer silicates, their swelling in water and organic liquids and interstratified layer structures. We come now to consider how this detailed information can be used to identify clay minerals. This means that we must consider how to prepare clay materials for X-ray examination. how to utilize X-ray diffraction equipment to obtain the necessary data, and finally how to compare these data with the accumulated information so as to arrive at an identification suitable for the purpose involved. Many aspects of sample preparation, of diffraction analysis, and of material identification apply to the study of crystalline materials generally. Here we shall emphasize those aspects which relate to the particular class of materials under consideration. It will be assumed that readers have access to books dealing generally with X-ray diffraction procedures, particularly powder methods of analysis; the following may be mentioned specifically: Elentents of X-Ray Diffraction, Cullity (1956, 1978); X-Ray Diffraction Procedures for Polycrystalline and Amorphous Materials, Klug and Alexander (1954, 1974).

No single identification procedure, not even X-ray diffraction, gives all the answers on all occasions. Consequently diffraction analysis is combined almost always with other methods, partly chemical and partly physical, Much depends on whether very detailed information is required on a few samples, or less detailed information on a very large number of samples. At one extreme, identification is more or less synonymous with mineralogical and crystallographic study of minerals; at the other extreme, it becomes one aspect of a broad geological or soil survey. In this chapter we enkavour to keep in mind this range of interests.