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1. Stishovite formation at very low pressures in soda-lime glass

   https://doi.org/10.1016/j.scriptamat.2019.06.005  

   Pozuelo, Marta; Lefebvre, Joseph; Srivastava, Pratyush; Gupta, Vijay (October 2019, Scripta Materialia)
2. Stishovite nucleation at low shock pressures in soda-lime glass

   https://doi.org/10.1016/j.actamat.2021.117124  

   Srivastava, Pratyush; Tanaka, Koichi; Ramirez, Brian; Gupta, Vijay (August 2021, Acta Materialia)
3. Evidence for the stability of ultrahydrous stishovite in Earth’s lower mantle

   https://doi.org/10.1073/pnas.1914295117  

   Lin, Yanhao; Hu, Qingyang; Meng, Yue; Walter, Michael; Mao, Ho-Kwang (December 2019, Proceedings of the National Academy of Sciences)

   The distribution and transportation of water in Earth’s interior depends on the stability of water-bearing phases. The transition zone in Earth’s mantle is generally accepted as an important potential water reservoir because its main constituents, wadsleyite and ringwoodite, can incorporate weight percent levels of H₂O in their structures at mantle temperatures. The extent to which water can be transported beyond the transition zone deeper into the mantle depends on the water carrying capacity of minerals stable in subducted lithosphere. Stishovite is one of the major mineral components in subducting oceanic crust, yet the capacity of stishovite to incorporate water beyond at lower mantle conditions remains speculative. In this study, we combine in situ laser heating with synchrotron X-ray diffraction to show that the unit cell volume of stishovite synthesized under hydrous conditions is ∼2.3 to 5.0% greater than that of anhydrous stishovite at pressures of ∼27 to 58 GPa and temperatures of 1,240 to 1,835 K. Our results indicate that stishovite, even at temperatures along a mantle geotherm, can potentially incorporate weight percent levels of H₂O in its crystal structure and has the potential to be a key phase for transporting and storing water in the lower mantle. 

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4. Elasticity of Hydrated Al‐Bearing Stishovite and Post‐Stishovite: Implications for Understanding Regional Seismic V _S Anomalies Along Subducting Slabs in the Lower Mantle

   https://doi.org/10.1029/2021JB023170  

   Zhang, Yanyao; Fu, Suyu; Karato, Shun‐ichiro; Okuchi, Takuo; Chariton, Stella; Prakapenka, Vitali B.; Lin, Jung‐Fu (April 2022, Journal of Geophysical Research: Solid Earth)
5. Behavior of Hydrogarnet‐Type Defects in Hydrous Stishovite at Various Temperatures and Pressures

   https://doi.org/10.1029/2022JB024980  

   Palfey, William R.; Rossman, George R.; Goddard, III, William A. (January 2023, Journal of Geophysical Research: Solid Earth)

   Abstract Dense polymorphs of silica have been demonstrated experimentally to incorporate from 1.5 wt% to as much as 11.6 wt% H₂O as OH groups, with implications for the hydrogen budgets of Earth and other planets. This OH is thought to enter the SiO₂structure via a charge‐balanced substitution in which silicon vacancies (V_Si) are compensated by protonating four of the surrounding six oxygen atoms, often referred to as a hydrogarnet‐type defect. There are many possible configurations for this defect structure in dense silica, but the nature of these configurations and whether they can be distinguished experimentally is unknown. We present here density functional theory calculations that systematically assess the possible configurations of a hydrogarnet‐type defect in stishovite (rutile‐type SiO₂), with direct comparisons to experimental vibrational spectroscopy data. We predict that stishovite synthesized at 450 K and 10 GPa quenched to room temperature is dominated by a single defect type with tetrahedral geometry. This leads to OH stretching modes (2,500–3,000 cm⁻¹) and SiOH bending modes (∼1,400–1,450 cm⁻¹) largely consistent with experimentally observed modes. One remaining issue is that our calculations produce results compatible with experimental data on H to D exchange, but do not explain why a considerable fraction of the 1,420 cm⁻¹mode shifts by only 40 cm⁻¹in deuterated samples. At elevated pressures and temperatures, we find that a second square planar defect configuration also becomes favorable, leading to modes that should allow differentiation from the tetrahedral configuration. 

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