Previous experiments at ENGIN-X (Wenk et al. 2007) established that quartz rocks undergo mechanical twinning if stressed above 100 MPa. The amount of twinning is highly temperature dependent and, at 500C, saturates at 400MPa. These in situ observations allow us to quantify the twinning process and to use the twinning pattern expressed in preferred orientation as a piezometer to enravel the deformation history of quartz-bearing rocks. Some important questions are unresolved: What is the influence of time on twinning? We propose an experiment at constant stress (e.g. 300MPa) to determine if twinning changes. We also want to investigate twinning patterns if material with no initial preferred orientation is cycled through the trigonal-hexagonal-trigonal phase transformations (at 573C) under stress. Cylindrical samples will be compressed and spectra will be analyzed with the Rietveld method.