Nanosecond structural evolution in shocked coesite

The phase transitions in minerals under shock are crucial for understanding meteorite impact history. Recent time-resolved x-ray diffraction (XRD) studies on silica shocked to 65 GPa proposed the formation of different high-pressure phases between fused silica and quartz. Furthermore, the dynamics of silica behavior under higher pressure need to be investigated, particularly during nonequilibrium superheating before melting. This study examines the time-dependent response of coesite, using laser-driven shock coupled with fast XRD and molecular dynamics simulations with our recently developed machine learning interatomic potential. Our results reveal a transient dense supercooled liquid crystallizes into a semi-disordered d-NiAs-type silica, followed by transforming into either seifertite or stishovite, depending on the pressure. Instead of thermodynamically stable quartz, a back-transformation to coesite phase is identified after release. The complicated phase evolution pathways in shocked coesite provide deeper insights into the high-pressure silica phases observed in the meteorite bombardments on the early Moon, Mars, and Earth.