Raman spectroscopy of water-rich stishovite and dense high-pressure silica up to 55 GPa

Nisr, Carole; Shim, Sang‐Heon; Leinenweber, Kurt; Chizmeshya, Andrew

doi:10.2138/am-2017-5944

Cited by 28 publications

(40 citation statements)

References 56 publications

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“…The water content of hydrous stishovite is estimated from the calibration presented in Nisr et al [] which is updated from the calibration used in Spektor et al []. If we use the calibration by Spektor et al [], we obtain 2.7 wt % for the water content.…”

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

“…Our sample synthesized at 9 GPa and 450°C contains 3.2 ± 0.5 wt % water based on the relationships from Nisr et al []. The calibration reported in Nisr et al [] was conducted using the data in Spektor et al [, ] (additional information on the determination of the water content can be found in the supporting information). Considering the errors from the synthesis pressure and temperature determination for our sample and Spektor et al [] sample, the water content we found is in the same order of magnitude of that of Spektor et al [] and is much higher than the water content previously reported in Al‐free stishovite (72 ppm) [ Bolfan‐Casanova et al , ] and in Al‐bearing stishovite (82–2900 ppm) [ Pawley et al , ; Chung and Kagi , ; Panero et al , ; Litasov et al , ].…”

Section: Resultsmentioning

confidence: 99%

“…We synthesized the sample at 9 GPa and 450°C for 49 h (Table ). Excess H 2 O was found after the experiment, indicating that silica was exposed to free H 2 O throughout the synthesis (further information on the synthesis method can be found in Nisr et al []). Optical observation indicated a grain size of ∼1 μm.…”

Section: Experimental Methodsmentioning

confidence: 99%

“…The spectra for the starting stishovite sample were collected for a few minutes. We report the interpretation of the 1 bar spectra and high‐pressure spectra of the sample in Nisr et al [].…”

Section: Experimental Methodsmentioning

confidence: 99%

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Phase transition and equation of state of dense hydrous silica up to 63 GPa

et al. 2017

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Although it has previously been considered to be essentially anhydrous, Al‐free stishovite can contain up to ∼1.3 wt % of H2O, perhaps through the direct substitution ( Si4+→4normalH+), according to recent studies. Yet the stability of such substitution and its impact on the properties of silica and rutile‐structured hydrous phases (such as δ‐AlOOH and phase H) are unknown at the conditions of the deeper mantle. We have synthesized hydrous and anhydrous Al‐free stishovite samples at 723 K and 9 GPa, and 1473 K and 10 GPa, respectively. Synchrotron X‐ray diffraction patterns show that the unit cell volume of hydrous stishovite is 1.3% greater than that of anhydrous stishovite at 1 bar, suggesting significant incorporation of OH in the crystal structure (3.2 ± 0.5 wt % H2O). At 300 K, we found a lower and broader transition pressure from rutile type to CaCl2 type (28–42 GPa) in hydrous dense silica. We also found that hydrous silica polymorphs are more compressible than their anhydrous counterparts. After the phase transition, the unit cell volume of hydrous silica becomes the same as that of anhydrous silica, showing that the proton incorporation through a direct substitution can be further stabilized at high pressure. The lower pressure transition and the pressure stabilization of the proton incorporation in silica would provide ways to transport and store water in the lower mantle in silica‐rich heterogeneities, such as subducted oceanic crust.

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Section: Resultsmentioning

confidence: 99%