TY - JOUR
T1 - Ultrahydrous stishovite from high-pressure hydrothermal treatment of SiO 2
AU - Spektor, Kristina
AU - Nylen, Johanna
AU - Stoyanov, Emil
AU - Navrotsky, Alexandra
AU - Hervig, Richard
AU - Leinenweber, Kurt
AU - Holland, Gregory P.
AU - Häussermann, Ulrich
PY - 2011/12/27
Y1 - 2011/12/27
N2 - Stishovite (SiO 2 with the rutile structure and octahedrally coordinated silicon) is an important high-pressure mineral. It has previously been considered to be essentially anhydrous. In this study, hydrothermal treatment of silica glass and coesite at 350-550°C near 10 GPa produces stishovite with significant amounts of H 2O in its structure. A combination of methodologies (X-ray diffraction, thermal analysis, oxide melt solution calorimetry, secondary ion mass spectrometry, infrared and nuclear magnetic resonance spectroscopy) indicate the presence of 1.3 ± 0.2 wt% H 2O and NMR suggests that the primary mechanism for the H 2O uptake is a direct hydrogarnet-like substitution of 4H + for Si 4+, with the protons clustered as hydroxyls around a silicon vacancy. This substitution is accompanied by a substantial volume decrease for the system (SiO 2 + H 2O), although the stishovite expands slightly, and it is only slightly unfavorable in energy. Stishovite could thus be a host for H 2O at convergent plate boundaries, and in other relatively cool high-pressure environments.
AB - Stishovite (SiO 2 with the rutile structure and octahedrally coordinated silicon) is an important high-pressure mineral. It has previously been considered to be essentially anhydrous. In this study, hydrothermal treatment of silica glass and coesite at 350-550°C near 10 GPa produces stishovite with significant amounts of H 2O in its structure. A combination of methodologies (X-ray diffraction, thermal analysis, oxide melt solution calorimetry, secondary ion mass spectrometry, infrared and nuclear magnetic resonance spectroscopy) indicate the presence of 1.3 ± 0.2 wt% H 2O and NMR suggests that the primary mechanism for the H 2O uptake is a direct hydrogarnet-like substitution of 4H + for Si 4+, with the protons clustered as hydroxyls around a silicon vacancy. This substitution is accompanied by a substantial volume decrease for the system (SiO 2 + H 2O), although the stishovite expands slightly, and it is only slightly unfavorable in energy. Stishovite could thus be a host for H 2O at convergent plate boundaries, and in other relatively cool high-pressure environments.
KW - High-pressure synthesis
KW - Hydrothermal environments
KW - Low temperature
KW - Multianvil technique
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U2 - 10.1073/pnas.1117152108
DO - 10.1073/pnas.1117152108
M3 - Article
C2 - 22160677
SN - 0027-8424
VL - 108
SP - 20918
EP - 20922
JO - Proceedings of the National Academy of Sciences of the United States of America
JF - Proceedings of the National Academy of Sciences of the United States of America
IS - 52
ER -