CLAY minerals are of widespread occurrence and only rarely are nataral materials pure. Usually other minerals are found in intimate association with the clay minerals and this chapter aims to provide a convenient collection of powder data that will allour thc identification of minerals commonly associated with clays. As these associated minerals frequently comprise only a small fraction of the sample, often only their more intense reflections can be observed but usually their response to the diagnostic treatments used for identifying clay minerals and a knowledge of the origin and history of the material makes possible reasonably certaln identifications. By contrast with other chapters of this book it is not the intention here to discuss crystal structures in any detail; the aim is to provide information for identifying the more common constituents associated with phyllosilicate clay minerals.
The Powder Diffraction File (PDF) published by the Joint Committee on Powder Diffraction Standards, 1601 Park Lane, Swarthmore. Pennsylvania 19081, U.S.A., provides an extensive and increasingly authoritative source of powder diffraction data and i: has been drawn upon heavily in the preparation of this chapter. For the oxides and hydroxides of iron and aluminium, Rooksby (1961) has been a valuable source. For information on manganese oxides the author is indebted to R. M. Taylor and R. M. McKenzie, Division of Soils, C.S.I.R.O., Glen Osmond, South Australia.
Probably the commonest accessory minerals in clays are the various hydroxides, oxyhydroxides and oxides of iron and aluminium. They are of major importance in relation to the technology of obtaining alumina from bauxites.
Figures & Tables
In the years 1930—1950 clay mineral identification involved mainly a combination of X-ray powder diffraction and chemical analysis with some assistance from other techniques, notably differential thermal analysis. In the period 1950—1970 additional procedures have emerged including infrared analysis, electron optical methods and a variety of thermal methods. These procedures are now treated in other monographs sponsored by the Mineralogical Society and in many other publications. Despite the availability of other techniques, X-ray diffraction remains a basic tool for studying minerals and we hope that this monograph will continue to serve, as did the previous editions, both those concerned with the more academic aspects of clay mineralogy and also those, such as geologists, civil engineers and soil scientists, for whom identification and quantitative estimation of the minerals in natural clayey materials is a practical requirement.