Original paper

Origin of twist in 'gwindel' quartz crystals from the Alps: a transmission electron microscopy study

Cordier, Patrick; Heidelbach, Florian

European Journal of Mineralogy Volume 25 Number 2 (2013), p. 145 - 153

published: Mar 1, 2013

DOI: 10.1127/0935-1221/2013/0025-2271

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Abstract

Two twisted quartz crystals (gwindels) from the Alps were studied by transmission electron microscopy and large-angle convergent-beam electron diffraction (LACBED) to elucidate the twist mechanism. We found that torsion results from a distribution of straight screw geometrically necessary b = 1/3 〈2110〉 dislocations with a dislocation density of the order of 1010 m−2. This dislocation microstructure induces an Eshelby twist which can account for the observed twist of a few degrees per centimetre. This microstructure suggests that twisted gwindel quartz forms by the spiral growth mechanism which enables crystal growth under small driving forces.

Keywords

twisted quartzgwindelgeometrically necessary dislocationsscrew dislocationstransmission electron microscopycrystal growth