• journal_title：European Journal of Mineralogy
• Contributor：Patrick Cordier ; Florian Heidelbach
• Publisher：E. Schweizerbart'sche Verlagsbuchhandlung Science Publishers
• Date：2013-02-01
• Format：text/html
• Language：en
• Identifier：10.1127/0935-1221/2013/0025-2271
• journal_abbrev：Eur J Mineral
• issn：0935-1221
• volume：25
• issue：2
• firstpage：145
• section：Articles

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 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.