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Quantitative 29Si NMR spectra of single-crystal [Alpha]-quartz, shock compressed to 12-38 GPa and recovered, provide new information about the complex response of quartz to shock loading. Spectra from samples recovered from shock pressures of 12-20 GPa show a broadening of the 29Si NMR peak and the development of asymmetry toward lower NMR frequency (indicating an increase in the mean Si-O-Si intertetrahedral bond angle). NMR spectra of samples shock compressed above [approximately]25 GPa show increasing amounts of a separate amorphous phase of Si[O.sub.2] with a mean Si-O-Si bond angle roughly 5 [degrees] narrower, and 10-15% denser, than fused Si[O.sub.2]. Small amounts of crystalline material remain with a mean Si-O-Si bond angle up to 3 [degrees] larger than unshocked [Alpha]-quartz. The recovery of dense glass indicates that post-shock temperatures were sufficiently low to also preserve stishovite, had any been created in our experiments. The paucity of stishovite or [6]Si in an amorphous phase in our recovered samples suggests that the formation of stable, high-coordinated Si is kinetically hindered in shock compression experiments up to about 3540 GPa, except in regions of high temperature, such as planar deformation features (PDFs), microfaults (pseudotachylites), or voids.

Quantitative 29Si NMR spectra of single-crystal [Alpha]-quartz, shock compressed to 12-38 GPa and recovered, provide new information about the complex response of quartz to shock loading. Spectra from samples recovered from shock pressures of 12-20 GPa show a broadening of the 29Si NMR peak and the development of asymmetry toward lower NMR frequency (indicating an increase in the mean Si-O-Si intertetrahedral bond angle). NMR spectra of samples shock compressed above [approximately]25 GPa show increasing amounts of a separate amorphous phase of Si[O.sub.2] with a mean Si-O-Si bond angle roughly 5 [degrees] narrower, and 10-15% denser, than fused Si[O.sub.2]. Small amounts of crystalline material remain with a mean Si-O-Si bond angle up to 3 [degrees] larger than unshocked [Alpha]-quartz. The recovery of dense glass indicates that post-shock temperatures were sufficiently low to also preserve stishovite, had any been created in our experiments. The paucity of stishovite or [6]Si in an amorphous phase in our recovered samples suggests that the formation of stable, high-coordinated Si is kinetically hindered in shock compression experiments up to about 3540 GPa, except in regions of high temperature, such as planar deformation features (PDFs), microfaults (pseudotachylites), or voids.