Quartz crystal twinning under mechanical stress: experimental measurements

To study the influence of parameters as quartz origin or crystallographic orientation on the ferrobielastic twinning in quartz, we discuss here some observations using stress-strain experiments on various samples. They have been prepared in different kinds of quartz crystals (natural and synthetic issued from three different origins) and with different orientations such as X- and AT-cut. The experiments have been carried out using an uniaxial stressing equipment for which the stress is applied in a suitable direction of the quartz sample. Infrared absorption spectroscopy (IR) and the Ion Coupled Plasma spectrometry (ICP) were used to characterize the contents of OH and metallic impurities associated to the quartz lattice. We report that X-cut samples exhibit stripe-shaped patterns with walls parallel to the optical axis while rather irregular domains expand in AT-cut samples. We notice that the twinned domain does not disappear after putting off the pressure. Furthermore, it has been observed that the stress level associated to the transition of twin domains are smaller for synthetic quartz than for natural one. Finally, we compare our theoretical point of view based on the Gibbs free energy function with experimental measurements performed on X-cut samples in which the stress is applied along different orientations