Equation of state of stishovite and interpretation of SiO2 shock‐compression data

We present an isothermal equation of state for the high‐pressure stishovite phase of SiO2 based on synchrotron X‐ray diffraction at 300 K to 60 GPa. The inferred equation of state is the same for stishovite synthesized from pure SiO2 glass as from a natural, basalt glass that forms stishovite in association with other mineral phases, yielding a zero‐pressure bulk modulus K0T = 312.9(±3.4) GPa and pressure derivative K′0 = 4.8(±0.2). Our measurements of stishovite at static, high pressures predict a shock‐compressed (Hugoniot) state that is 2.4 (±1.6)% denser than observed for SiO2, suggesting that an amorphous phase, rather than stishovite, is produced under impact loading.