Characterization of poorly ordered minerals by selective chemical methods

At the beginning of this century, ideas on the composition of clay-size material were greatly influenced by van Bemmelen (1910) who suggested that this material existed as a completely amorphous colloidal complex. However, many mineralogists thought that clays could be a mixture, containing varying proportions of crystalline material (Mackenzie, 1963). The mixed-oxide hypothesis of van Bemmelen (1910), associating the colloidal state with non-crystallinity persisted until Hendricks and Fry (1930), using X-ray methods showed the presence of large amounts of crystalline material in soil clays. This resulted in the virtual rejection of ideas advocating an amorphous nature for clays. Also, researches were directed almost exclusively towards elucidation of the physico-chemical reactions within the crystal structure of clay minerals. Despite this emphasis on crystallinity, Mattson, in a series of papers on the colloidal chemistry of soil, continued to recognize the importance of inorganic, poorly ordered components in soils — a balanced view which has now become generally accepted (Rich and Thomas, 1960; Mitchell, Farmer and McHardy, 1964). Soil clay can, therefore, best be regarded as consisting of both crystalline and non-crystalline minerals.