An electron-diffraction study of a microcrystalline muscovite and its vermiculitized products

Abstract

SummaryAfter approximately 50% of K from the 1–2 μm fraction of a naturally occurring microcrystalline muscovite was extracted with BaCl2 solution at 98°C electron-diffraction patterns showed a honeycomb-shaped diffuse scattering as well as intense diffuse streaks. The diffuse scattering became pronounced with increasing K-depletion. It may be interpreted in terms of a short-range order distribution of interlayer Ba ions, using an analogy to the work by Alcover et al. (1972, 1976). Since the diffuse streaks still remained after re-entry of K to the K-depleted specimen they might be related to structural disturbance, particularly in the basal oxygen arrangements, resulting from the K-extraction. Subsequent conversions of Ba-saturated vermiculitized muscovite into Na-, Mg-, and Ca-forms revealed distinct extra diffraction spots midway between two ordinary diffraction spots. They were broader than the ordinary spots and elongated along the three directions of [01]*, [11]*, and [11]*. The diffraction pattern containing the extra spots was, therefore, interpreted as a composite one made up by superimposing three independent patterns, each of which was composed of ordinary Bragg diffraction spots and extra diffraction maxima elongated in one of the three directions. This situation does not require a superlattice but modified the original face-centred lattice symmetry to a primitive lattice symmetry. However, the presence of a real superlattice should also be possible. The elongation and broadness of the extra diffraction maxima may be related to the orientation and size of coherent domains defined by a certain ordering of interlayer cationic distribution, which took place during the hydration processes including extraction and conversion.

Electron Diffraction and High-Resolution Electron Microscopy of Mineral Structures

“…A similar distribution of diffuse spots was observed for vermiculitized muscovite with residual interlayer K by Kodama (1977) who analyzed X-ray diffuse scattering.…”

“…84 will be given after discussing the results obtained by other authors (Suquet 1978;Kodama 1977;Moret et al 1976;Ridder et al 1976Ridder et al , 1977a. 84 will be given after discussing the results obtained by other authors (Suquet 1978;Kodama 1977;Moret et al 1976;Ridder et al 1976Ridder et al , 1977a.…”

Comments on the Classification of Trioctahedral 2:1 Phyllosilicates

“…Mrring and Prdro (1969) proposed this criterion on the basis of a correlation made between diffuse scattering linking certain Bragg reflections together and a postulated distribution of A1 substitutions along chains in muscovite. This type of diffusion has since been observed in smectites and micas and is apparently produced by fluctuations of the position of the surface oxygen atoms around their equilibrium points (Kodama, 1977). Besson et al (1974) based the "order vs. disorder" of cationic substitutions on the interpretation of honeycomb-shaped diffusion that is observed only in vermiculites and micas.…”

Parameters Influencing Layer Stacking Types in Saponite and Vermiculite: A Review

“…It was also observed in muscovite-2M, by Gatineau (1964), in Ba-montmorillonite and synthetic Ba-beidellite by Besson et al (1973Besson et al ( , 1974a, and in natural Ba-beidellite by Giiven et al (1977). Because this type of scattering occurs for unsubstituted phyllosilicates such as talc and pyrophyllite (Kodama, 1975(Kodama, , 1977, it can no longer be considered to be an indicator of order and disorder of cationic substitutions and of interlayer cations. The diffusions can be interpreted either as thermal diffusions or as the trace of planar diffusions that correspond to linear distortions in the direct structure perpendicular to the diffusion planes.…”

“…In the latter, the distortions would appear as "chains" in the [ 10] direction and along the two other 120 ~ axes. Inasmuch as these three directions are in fact those of the surface oxygen atoms, and because their z value exhibits significant fluctuations, we postulate, as did Kodama (1975Kodama ( , 1977, that the diffuse scattering which links certain reflections is produced by fluctuations of the position of the surface oxygen atoms around their equilibrium position. These fluctuations are static or dynamic.…”