ABSTRACT
Staining techniques have been used since the nineteenth century for the identifi cation of biological and mineralogical materials. The adsorption of various or ganic substances by natural and chemically altered or heat-treated clays can pro duce color changes in the clay. These changes depend on the identity of the clay mineral and its composition. The color changes, therefore, provide a possible basis for identification and quantitative determination of the clay mineral compo nent of clay and other materials. They also provide a tool for the study of certain surface properties, such as surface acidity, oxidizing-reducing sites, cation ex change capacities, and colloidal properties. A staining test has the advantage of being rapid and simple to perform, even in the field. The subject was reviewed by Mielenz and King (1951), Grim (1968), Theng (1971), and Solomon and Haw thorne (1983). Since the publication of these reviews, many studies of staining have been performed by modem techniques. Among these techniques visibleabsorption spectroscopy study gives the most significant information on staining (Schoonheydt, 1981) and will be reviewed in this chapter. Thermal analysis, in frared (IR) spectroscopy, fluorescence spectroscopy, and electron spin resonance (ESR) also give important information on staining. The first two are fully treated in other chapters of this book, and the last two will be briefly mentioned here.
