| Abstract: | The polytypism of pyrophyllite as a special phyllo-silicate is investigated by means of high resolution electron microscopy (HREM), supported by computer simulation. Electron micrographs of appropriate specimen orientations provide crystal structure images, which reveal the actual stacking sequence of the silicate layers. Two crystallographic models (2M1- and 1Tc-type) are applied for the numerical simulation of the image contrast. The process of the electron scattering in the crystal as well as the influence of the imaging parameters are described by means of multi-slice image calculations. The strong effect of through-focusing to the image contrast of the silicate structure is pointed out. |
