Abstract
FOR fifty years or more a number of people of have been endeavouring to give a satisfactory answer to the question, “What is clay?” Instead of a simple answer which meets all requirements, no adequate definition has been found. Geologists define as clay many substances which potters would reject. Chemists look for a definition based on chemical composition and fail to obtain satisfaction because many commercially useful ‘clays’ differ so greatly in composition that no satisfactory correlation seems possible. The highly plastic blue clay used by glove manufacturers seems to have little in common with the hard grey fireclays of the Coal Measures and even less with the china clays of Devon and Cornwall, or the kaolin of the text-books. Plasticity—which is supposed by many people to be the chief characteristic of all clays—is almost absent from some kaolins the composition of which causes them to be regarded as the purest of all clays and the ‘typical clay-substance’ of numerous authors and investigators. On the other hand, many substances become plastic when suitably treated, though their compositions are so different from any kind of clay that the inclusion of plasticity as an essential part of any definition has often led to confusion.
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References
Z. Kryst., 97, 216 (1937).
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SEARLE, A. Clay. Nature 141, 583–585 (1938). https://doi.org/10.1038/141583a0
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DOI: https://doi.org/10.1038/141583a0