Three-layer monoclinic 3M2 polytype of muscovite revealed from oblique-texture electron diffraction patterns

The inhomogeneous (complex) polytype 3M2 of finely dispersed muscovite with the structure formed by layers with different parity of azimuthal orientations (561) or relative rotations \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document} $$[11\bar 2]$$ \end{document} was identified for the first time using the oblique-texture electron diffraction patterns. The specimen had no rigorous order in layer alternation, which is reflected in the distortion of the reflection positions and intensities. It is shown that the most probable defects reduce to the replacement of the layer orientations characteristic of the 3M2 polytype by layer orientation characteristic of the 2M2 polytype. This fact indicates that, under certain conditions, the prismatic coordination of interlayer cations in micas is preferable.