Properties of the Quartz A-B transition at High Pressure

Quartz, one of the main constituents of the Earth’s crust, undergoes a phase transition (-) with increasing temperature. However, the temperature at which this transition occurs at high pressure and its very nature, i.e., whether it is a first or a second order, merely displacive, transformation is not clear. In addition, thermodynamics databases predict a dramatic increase in compression wave velocity, Vp in the  field with depth, which results in the attribution of high velocity zones in seismic tomography data to the - transition. Therefore, an accurate characterization of the pressure and temperature (PT) position of the transition and the associated velocity changes will provide valuable data for the interpretation of seismic velocities. Here, we propose to investigate the cell parameters of - quartz at ID06 to relate PT to phase change. XRD data will be combined to measurements of ultrasonic velocities to track the evolution of Vp across the transition.