Evidence of Texture on the Origin of the Cheltenham Fireclay of Missouri and Associated Shales

ABSTRACT The Cheltenham fire clay of Missouri is relatively massive in structure while typical shale, exemplified by the Lagonda, is laminated. The microscopical texture of the Cheltenham fire clay is a pattern of clay minerals grown in random directions, whereas that of the associated shale is an oriented arrangement of clay-mineral flakes which lie parallel to the lamination. It is deduced that the Cheltenham fire clay was developed from redeposited weathered-soil clay and further hydrolyzed and dialyzed in nearly stagnant water of Pennsylvanian swamps. The crystals of the fire-clay minerals grew at random in this clay gel. Many shales, on the other hand, are believed to have been deposited directly after flocculation without a significant interim period of leaching. The clay floccule, having a flaky shape, settled to the bottom where countless other clay flakes in the same orientation gave rise upon compaction to a conventional laminated shale. Possibly these criteria may be extended more generally to other argillaceous rocks.