Polytypic Constraints for Solid-State Layer Silicate Transformation Mechanisms Via Atomic-Resolution Transmission Electron Microscopy

Abstract

Abstract Layer silicates are important and abundant minerals. Polytypic details can be determined directly from atomic-resolution images recorded down [010] of layer silicates such as chlorite (Fig. 1), serpentine, and micas using a transmission electron microscope with a point resolution of ∼ 0.2 nm. For chlorite, this involves determination of whether octahedral slants in the brucite-like interlayers and octahedral sheet of the tetrahedral - octahedral-tetrahedral (TOT) layers are the same or opposed, the (3 angle, and how the octahedral cations in the brucite-like interlayer are positioned relative to the tetrahedral cations in the TOT layer (Fig. 1). Images must be recorded from the thinnest areas in order to distinguish slant of the brucite-like interlayer (composition dependent, but always < 0.7 nm sample thickness; 1). Polytype analysis is aided significantly by rotational filtering of images from thin areas to remove the amorphous contribution (2). All six of the common, semi-randomly stacked chlorite polytypes can be distinguished (1).