Volume 1 (1972), Issue 1, Pages 1-8
The Texture of a Slate From Nantlle, Caernarvon, North Wales
1Department of Geology, University of California, Los Angeles, California, USA
2Department of Physics, University of California, Berkeley, USA
3Department of Physics, Monash University, Melbourne, Australia
Received 13 December 1971
Copyright © 1972 Hindawi Publishing Corporation. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
A specimen of Cambrian slate from the slate belt in North Wales has been thinned by the ion bombardment technique to produce an ultrathin section with the specimen plane normal to the cleavage plane. This specimen has been investigated with the electron microscope by electron transmission. Selected area diffraction patterns allow identification of individual sheet silicate grains. The pole figures of the basal planes of two sheet silicate minerals, muscovite and chlorite, have been measured with an X-ray pole-figure goniometer and both show an elongated maximum normal to the slaty cleavage, with orthorhombic symmetry. While the preferred orientation could be the result of mechanical rotation of rigid flakes in a deforming matrix, the texture (the overall pattern due to the shapes and sizes of grains and their angular relations to each other) can only be explained if considerable recrystallization is assumed. It is tentatively proposed that local dissolution at points of stress-concentration with simultaneous redeposition of the dissolved material in less stressed regions may have allowed closely packed grains to act as if they were mechanically rotating rigid flakes, yet to accommodate their shapes enough to prevent interlocking.