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Orientation of the boundaries of out-of-step domains in anorthite

Published online by Cambridge University Press:  14 March 2018

Paul H. Ribbe
Affiliation:
Department of Geological Sciences, Virginia Polytechnic Institute, Blacksburg, Virginia
Alan A. Colville
Affiliation:
Department of Geological Sciences, Virginia Polytechnic Institute, Blacksburg, Virginia

Summary

The orientation of the boundaries of out-of-step domains in ‘transitional’ anorthite has been deduced from the direction of elongation of the diffuse X-ray reflections h + h + l = 2n + 1 in selected precession photographs. The reflections are elongated normal to which is in the zone and contains the body-centring vector (a+b−c)/2. The structure is presumed to be perfect parallel to . Atoms in essentially identical, primitive anorthite-like domains are related across the out-of-step domain boundaries by body-centring vectors. Increasing diffuseness of the h + k + l = 2n + 1 reflections indicates progressively smaller domains (more frequent domain boundaries), and when thesereflections disappear, the structure has become body-centred on the average.

Type
Research Article
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1968

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