Regularly interstratified mica-smectites and chlorite-smectites have been synthesized by Ueda & Sudo (1966), Frank-Kamenetskij et al. (1972), Matsuda & Henmi (1973, 1974) and by Eberl (1978). Only a few studies have been carded out, however, on regularly interstratified minerals whose spacings exceed 30 Å (Lazarenko & Korolev, 1970; Sato & Kizaki, 1972).

A recent article by Refait & Génin (1997) was devoted to Ni(II)-Fe(II)-Fe(III) pyroaurite-like hydroxychlorides obtained by aerial oxidation of mixed Ni(II)-Fe(II) hydroxides with various P = Fe/Ni ratios in chloride-containing aqueous solutions. Corresponding to the ideal composition Ni3-xIIFexIIFeIII(OH)8Cl.nH2O , the Fe(III)/[Ni(II)+Fe(II)] ratio is 1/3 when P is >1/3. These hydroxyehlorides oxidize quickly and the final product depends on P. In the absence of nickel, P = ∞, FeII3FeIII(OH)8Cl.nH2O, known as Green Rust one (Bemal et al, 1959) oxidizes into γ-FeOOH. When P is >5/3, the X-ray diffraction (XRD) analyses of the end-product reveal lepidocrocite and some Ni(II)-Fe(III) hydroxychloride.

Outcrop samples of Ordovician K-bentonite from northeast Georgia were studied with X-ray diffraction (XRD) using different cation saturations to look for possible redistribution in layer charge. It was noted that XRD patterns of the samples responded uniquely to each cation treatment. The purpose of this note is to demonstrate a refinement to the method of Środoń (1980) for the precise identification of mixed-layer illite-smectite (I-S) and to note the importance of using several homoionic saturations in the interpretation of the XRD patterns.