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Structural analysis of twins in feldspars; I, Carlsbad twinning

Massimo Nespolo and Bernd Souvignier
Structural analysis of twins in feldspars; I, Carlsbad twinning
European Journal of Mineralogy (December 2017) 29 (6): 939-947

Abstract

In this article, we analyse the common substructure of the Carlsbad twin in terms of the (pseudo)-eigensymmetry of the crystallographic orbits. In the case of the monoclinic polymorphs, all the orbits in the highest subgroup compatible with the twin lattice possess a (pseudo)-eigensymmetry which contains a restoration operation corresponding to the twin operation, which implies a high degree of structural restoration. This structural restoration is realised for twin elements located at distance one half the length of the unit cell, which explains the high occurrence frequency of this twin and its occurrence as both contact and penetration twin, and as primary or synneusis twin. In the case of triclinic polymorphs, the common substructure is much less satisfactory and the Carlsbad twin is probably inherited from the monoclinic phases, accompanied by transformations twins, or by late-stage synneusis, where mechanical adherence on prominent faces plays a more fundamental role.


ISSN: 0935-1221
EISSN: 1617-4011
Serial Title: European Journal of Mineralogy
Serial Volume: 29
Serial Issue: 6
Title: Structural analysis of twins in feldspars; I, Carlsbad twinning
Affiliation: Universite de Lorraine, Cristallographie, Resonance Magnetique et Modelisations, Nancy, France
Pages: 939-947
Published: 201712
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Germany
References: 50
Accession Number: 2018-059623
Categories: Mineralogy of silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 4 tables
Secondary Affiliation: Radboud University Nijmegen, NLD, Netherlands
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute. Abstract, copyright, Schweizerbart'sche Verlagsbuchhandlung. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 2018
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