Applications of Transmission Electron Microscopy in Mineralogy

Abstract

The advent of X-ray analysis in the transmission electron microscopy (TEM) has helped in identifying fine-scale mineral phases, which would have been impossible or tedious to identify by electron diffraction, given the large unit cells, complex chemistry, and low symmetries that are involved in most cases. It is in the field of phase transformations that TEM has probably had the widest influence in mineralogy. It had long been known from the study of petrographic thin sections in the polarizing microscope that exsolution is common in the pyroxenes, amphiboles, and feldspars from slowly cooled rocks such as large igneous intrusions. In the 1950s and 1960s studies by single-crystal X-ray diffraction (XRD) were able to indicate the lattice orientations of these intergrowths and also to show that exsolution was present in many minerals. XRD could not, however, give any indication of the mechanisms of exsolution, nor, of the size of the precipitates or the orientation of their interfaces. This is where TEM has come into its own.