Stishovite Formation from Α-Quartz under Laser Shock Compression

The structural response of compressed α-quartz is important to understanding shock metamorphism in impact craters. Previous dynamic and static compression experiments have shown inconsistent pathways to forming stishovite, defective niccolite- (d-NiAs), rosiaite-type silica, and coesite below 40 GPa. Using laser shock compression and x-ray diffraction with an x-ray free-electron laser, we studied the time-resolved structural response in Z-cut single-crystal α-quartz at 9 and 38 GPa and polycrystalline quartzite at 38 GPa. We observed the formation of stishovite and an amorphous phase on a timescale of 5-16 ns at 38 GPa, while at 9 GPa only strained α-quartz is observed. Our calculations further revealed that stishovite is energetically favored under faster timescales compared to d-NiAs, while coesite formation requires higher energy barriers and an intermediate phase, such that it is prohibited under dynamic conditions. The observed aggregate of stishovite and the amorphous phase is consistent with observations from impact craters, but differences in timescale and amorphous structure warrant caution in direct comparisons. Understanding the structural response of compressed α-quartz is crucial for insights into shock metamorphism in impact craters, yet previous studies have shown inconsistent pathways to forming high-pressure silica phases. Here, the authors use laser shock compression and x-ray diffraction to reveal that stishovite and an amorphous phase form rapidly at 38 GPa, providing insights into impact processes.