gsminmag Mineralogical Magazine Mineralogical Magazine 0026-461X Mineralogical Society 10.1180/minmag.1973.039.302.05 A Transmission Electron Microscope and X-ray Diffraction Study of Muscovite and Chlorite Oertel G. Curtis C. D. 1 Phakey P. P. 2 Department of Geology, University of California, Los Angeles, California

Permanent address: Department of Geology, The University, Sheffield S1 3JD, England.

Present address: Department of Physics, University of California, Berkeley, California. (Permanent address: Department of Physics, Monash University, Melbourne, Australia.)

 6 1973 39 302 176 188 23 6 1972 Copyright © 1973, The Mineralogical Society 1973 Summary

Single-crystal diffraction patterns produced by transmitted radiation, both X-rays and electrons, reveal varying degrees of disorder and long-range order in common phyllosilicates from several different rock types. The transmission electron micrographs and their selected-area diffraction patterns demonstrate the presence of numerous stacking faults parallel to (001) of muscovite and chlorite. Individual stacking faults can be recognized by the diffraction-contrast fringe patterns they cause, and partial dislocations can be seen where such faults terminate inside a crystal. Long-range order of muscovite explains what seemed to be spurious, high ‘background’ levels that are sometimes encountered in the analysis of rock fabrics by transmitted X-rays.