Mineral composition in relation to particle size for a Missouri plastic fire clay

From the rather modest beginning of the refractory industry in Missouri prior to the Civil War, the industry has grown to challenge those of other states as the third largest producer of refractory clays and products in the United States. As Roberts (1950) points out, the development of the metallurgical and glass industries increased the demand for high grade refractory materials. A prominent factor in the development of the fire clays of Missouri was the discovery that flint clay could be mixed with the plastic or semi-plastic refractory clays to yield an excellent product. Perhaps the most important reason many eastern manufacturers set up plants in Missouri is the close proximity to high quality plastic, semi-plastic, flint; and diaspore-clay deposits. Their rather shallow depth permits them to be extracted by economical open-pit methods which replaced the inefficient underground mining methods of the early 1920\u27s. As the refractory industry became big business, it adapted the futuristic outlook of big business. Common practice in the clay industry had been to stockpile only enough clay for immediate needs, as the cost of production included relatively high processing costs and the cost of the raw materials has to be kept to an absolute minimum. Clay deposits were discovered by examining outcrops exposed in stream banks and road cuts. Occasionally, someone drilling for water would discover a good clay. Now extensive scientific prospecting methods directed by technically trained personnel are employed (Bradley and Miller, 1942; W.D. Keller, 1949, pp. 451-454). While the importance of the high grade clay deposits of Missouri is generally recognized, the only extensive investigations published to date have been concerned with the distribution and genesis of the deposits. Very little work has been done regarding the detailed mineralogy of these clays. One has only to look at the works of Grim (1939a; 1939b, 1946) to get an appreciation of the importance minor clay constituents have on the properties of the whole clay. For example, montmorillonite leads illite and kaolinite, in that order, in properties of plasticity, drying shrinkage, bonding power and response to exchangeable bases. Even undetectable amounts of montmorillonite or illite in a kaolin may cause it to exhibit properties not common to kaolionite. Detailed investigation of these clays will help us to better understand some of their “unusual” properties. Results of these investigations may also be used to correlate various clay deposits on the basis of their clay mineral content after more information has been accumulated. There is still lacking in the literature enough information on clay mineral assemblages to develop uncontradictory paragenetic relations. In other words, clay mineral alteration sequences are still obscure. With these considerations in mind, the Department of Geology has set up a Clay Mineral Project, the purpose of which is to investigate more thoroughly the clay mineral content of Missouri clays and shales. This is the initial paper of the project. It purports to study the methods of investigating clays, to adapt standard methods to the facilities available, and to report the mineral content of a Missouri plastic refractory clay. It is hoped that this paper will stimulate interest in Missouri clays --Introduction, pages 1-3