Ferrobielastic twinning in quartz single crystals was investigated with regard to crystallographic orientation and crystal source. Complete volumetric transformation to the alternative Dauphiné twin state was achieved, in X- and AT-cut samples of natural and synthetic quartz, by applying a uniaxial compressive stress. Polarized-light or synchrotron-radiation X-ray topography was used to monitor the movement of twin boundaries. The dependence of the coercive stress and preferred orientation of twin boundaries upon the crystallographic orientation were explained in terms of the thermodynamic potential of the Gibbs free energy. When compared with natural crystals, the stress level for complete transformation to the alternative twin state was 30% lower for synthetic quartz. The results were qualitatively explained by the pinning of Dauphiné twin boundaries at randomly distributed impurity-related point defects. These were evaluated by means of infra-red spectroscopy and ion-coupled plasma spectrometry. The spontaneous irreversibility of ferrobielastic twinning upon unloading was confirmed.

The Roles of Crystallographic Orientation and Crystal Origin in Ferrobielastic Twinning of Quartz under Uniaxial Stress. P.L.Guzzo, J.J.Boy: European Physics Journal - Applied Physics, 2000, 12[1], 17-30