Lattice Perfection and Growth History of Doubly-Terminated Natural Alpha Quartz Crystals

A. R. Lang, A. P. W. Makepeace and M. Moore
H. H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol BS8 ITL, UK
Department of Physiology, School of Medicine, University of Bristol, Bristol BS8 1TD, UK
Department of Physics, Royal Holloway, University of London, Egham, Surrey TW20 0EX, UK

Abstract: Synchrotron X-ray topography was the principal perfection-assessment method employed. X-ray wavelengths were chosen that gave optimum penetration and diffraction contrast characteristics for the size of crystals examined. Two colourles transparent specimens were selected for comprehensive study. Both were of simple habit consisting of the prism {101¯0} terminated at each end by major and minor rhombohedral facets only. The larger specimen, volume ≈250 mm3, contained a moderately high but non-uniformly distributed dislocation population, totalling ≈103, all emanating from a roughly centrally located small nuclear volume. One apical region was dislocation-free. Optical microscopic observations including Nomarski interference contrast of features on one major rhombohedral facet in this region are described. The smaller specimen, volume ≈30 mm3, was remarkable for its low dislocation content, ≈20 in total, all radiating from a central point. Enhancement of dislocation image visibility relative to diffraction contrast images of severe surface damage on this crystal was demonstrated using higher-order X-ray reflections. Neither of the specimens studied in detail contained twinning or evident diffraction contrast from impurity zoning. Their lack of a microscopically visible or X-ray topographically detectable nucleating body favours a homogenous nucleation origin of these crystals.

Keywords: quartz • X-ray topography dislocations • growth history

Mineralogical Magazine; March 1994 v. 58; no. 390; p. 87-95; DOI: 10.1180/minmag.1994.058.390.09
© 1994, The Mineralogical Society
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