Quantitative X-ray Determinations of some Aluminous Clay Minerals in Rocks1

Leonard G. Schultz
U.S. Geological Survey, Denver, Colorado
1 Publication authorized by the Director, U.S. Geological Survey.

Abstract: X-ray diffraction traces were made of oriented aggregates of artificial binary mixtures containing approximately equal, weighed amounts of samples of illite, montmorillonite, mixed-layered combinations of illite and montmorillonite, and of kaolinite samples having different degrees of crystallinity. Measurements most suitable for quantitative purposes were obtained from the 7 Å kaolinite peaks and from the 10 Å peaks of illite and collapsed montmorillonite and collapsed mixed-layer clay. In this paper the sum of five height measurements at half-degree intervals across the peak are considered to be a measure of the area of the peak. Fireclay-type kaolinites gave 7 Å peak areas about equal to the area of the 10 Å peak of an equal amount of illite, montmorillonite, or mixed-layer clay, whereas well-crystallized kaolinites gave 7 Å peak areas generally about twice that of the 10 Å peak of an equal weight of the illite-montmorillonite minerals. Kaolinite samples having intermediate degrees of crystallinity gave 7 Å/10 Å peak area ratios intermediate between 1 : 1 and 2 : 1. The shape of the 7 Å kaolinite peak was used to evaluate the crystallinity of the kaolinite.

X-ray diffraction characteristics of the chlorite minerals from the different groups of sedimentary rocks studied vary considerably, and no uniform method has been found for their evaluation.

Clays and Clay Minerals; 1958 v. 7; no. 1; p. 216-224; DOI: 10.1346/CCMN.1958.0070113
© 1958, The Clay Minerals Society
Clay Minerals Society (www.clays.org)