Baseline Studies of the Clay Minerals Society Source Clays: Powder X-Ray Diffraction Analyses

The Clay Minerals Society maintains a repository of Source Clays to provide scientists and researchers with a readily available supply of consistent materials so that research conducted by different groups can be correlated to identical material. These Source Clays include kaolinite, smectite, chlorite, vermiculite, illite, palygorskite and other minerals. As most of the Source Clays are naturally occurring materials, they typically contain minor to significant amounts of other mineral impurities. When conducting research using these samples, it is important that their mineral content be well characterized. It is also often desirable to remove these impurities to produce pure clay samples. For example, when studying the biological effects of a particular clay mineral, it is imperative that all contaminants ( e.g. crystalline silica minerals) be removed from the clay in question so that experimental results can be attributed to the clay alone. If purification is required, the clays must be purified in a manner that does not significantly alter the physical or chemical properties of the samples. This chapter describes the X-ray diffraction (XRD) characteristics of a suite of Source Clays of The Clay Minerals Society and demonstrates methods of purification based on Stokes' law of settling in suspension that can be used to purify the clays.