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Treatment ofsmectite with laurylamine hydrochloride was verified to cause expansion of d(001) which may be retained and observed in ion-milled samples by transmission electron microscopy. The spacings between layers as observed in lattice fringe images, however, are variable and may be as small as 10 A. The method therefore produces ambiguities in differentiating between some smectites and illites, similar to those that have been found for untreated samples; e.g., on this basis, expanded layers may be inferred to be smectite, but layers with d-values approaching 10  may be either illite or smectite. Expansion also destroys the original rock texture, which, therefore, must be observed using only untreated samples.

Diffusion of K during analytical electron microscopy (AEM) results in anomalously low count rates for this element. As the analysis area and specimen thickness decrease, count rates become dispro- portionally lower. Adularia and muscovite show different diffusion profiles during AEM; for muscovite a strong dependence of diffusion on crystallographic orientation has been observed. Conditions giving rise to reliable chemical data by AEM are the use of a wide scanning area (>800 x 800 A) and/or large beam size to reduce the effect of diffusion of alkali elements, a specimen thickness greater than about 1000 ~, constant instrument operating conditions, and the use of a homogeneous, well-characterized standard sample. The optimum thickness range was obtained by determining the element intensity ratio vs. thickness curve for given operating conditions. The standard and unknown should have a similar crystal structure and, especially for strongly anisotropic minerals such as phyllosilicates, a similar crys- tallographic orientation with respect to the electron beam.