Adjustment of Clays to Chemical Change and the Concept of the Equivalence Level

Maurice C. Powers
Shell Oil Company, Houston, Texas

Abstract: Further x-ray and chemical work on suspended sediment samples and cored samples from the James River and its estuary support earlier proposals by the author. A chlorite-like clay is forming from weathered illite through a mixed-layer illite-vermiculite-chlorite stage, and some illite is seemingly regenerated to a better illite by potassium fixation.

Chemical analyses of interstitial water, hydrochloric acid-leachate, and fused samples offer explanations regarding the chemical changes occurring in clays as composition of the environment changes.

Magnesium is adsorbed by clays to a far greater degree than potassium in the marine and brackish environment.

The variance between clays found in Recent and ancient sediments is related to and explained by the concept of the equivalence level. It is suggested that K+ is adsorbed preferentially to Mg2+ by clays when they have been buried to a depth that is greater than that of the Mg2+ − K+ − equivalence level; above this level Mg2+ is preferentially adsorbed by the clays.

The trifold nature of clay minerals in terms of their origin and distribution is briefly discussed.

Clays and Clay Minerals; 1957 v. 6; no. 1; p. 309-326; DOI: 10.1346/CCMN.1957.0060123
© 1957, The Clay Minerals Society
Clay Minerals Society (www.clays.org)