AP42 Section: Reference: Title: 11.25 Clays, S. H. Patterson and H. H
AP42 Section: 11.25 Reference: ~ Title: Clays, S. H. Patterson and H. H. Murray, Industrial Minerals And Rocks, Volume 1, Society Of Mining Engineers, New York, 1983. The term clay is somewhat ambiguous un- less specifically defined, because it is used in three ways: (I) as a diverse group of fine- grained minerals, (2) a5 a rock term, and (3) as a particle-size term. Actually, most persons using the term clay realize that it has several meanings, and in most instances they define it. As a rock term, clay is difficult to define be- cause of the wide variety of materials that com- ,me it; therefore, the definition must be gen- 'eral. Clay is a natural earthy, fine-grained ma- Iterial composed largely of a group of crystalline ;minerals known as the clay minerals. These minerals are hydrous silicates composed mainly of silica, alumina, and water. Several of these minerals also contain appreciable quantities of iron, alkalies, and alkaline earths. Many defini- tions state that a clay is plastic when wet. Most clay materials do have this property, but some clays are not plastic; for exaniple, halloysite and flint clay. As a particle-size term, clay is used for the category that includes the smallest particles. The maximum-size particles in the clay-size grade are defined differently on various grade scales. Soil imestigators and mineralogists gen- erally use 2 micrometers as the maximum size, whereas the widely used scale by Wentworth (1922) defines clay as material finer than ap proximately 4 micrometers. Some authorities find it convenient to'use the term clay'for any fine-grained, natural, earthy, argillaceous material (Grim.
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