Potassium Content of Illite

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Science  05 Feb 1965:
Vol. 147, Issue 3658, pp. 603-605
DOI: 10.1126/science.147.3658.603


The average potassium oxide content of 18 Paleozoic two-layer monoclinic illites is 8.75 percent. There is an excellent linear relation between the ratio of the intensities of the reflections at 10 angstroms and 5 angstroms (10 Å/5 Å) and the potassium oxide content. The frequency distribution curve of the 10 Å/5 Å intensity ratio of 249 Paleozoic illite-rich shales is approximately normal. The modal value is 2.0, equivalent to 9.3 percent potassium oxide, and the average ratio is 2.47, equivalent to approximately 8.5 percent potassium oxide. The illite layers of many of the mixed layer illites-montmorillonites have from 8 to 10 percent potassium oxide. With a minimum number of assumptions realistic structural formulas for the two members of a mixed-layer illite-montmorillonite can be calculated.