The crystalline-to-amorphous transformation in the solid state is currently the subject of intense study. With the seminal discovery of amorphization of H2O ice I under pressure1, interest has focused on the possible occurrence of pressure-induced amorphization in other systems, the thermodynamic and mechanistic basis of the process, and the relationship between amorphization by pressure and by other means2-5. Here we report in situ synchrotron X-ray diffraction measurements of α-quartz and coesite in a diamond-anvil cell that demonstrate that these crystalline materials transform to amorphous solids at 25-35 GPa and 300 K. We show that an internally consistent thermodynamic description of the process is possible, extending into the pressure domain recent thermodynamic calculations of thermally-induced amorphization of silica polymorphs4. The measurements provide constraints on the equations of state and melting relations in this system at high pressures, shed light on the mechanism for glass formation in SiO2 in laboratory shock-wave experiments and meteorite-impact events, and provide insights into the thermoelastic stability of tetrahedral network structures at high compression.
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