期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2011
卷号：108
期号：52
页码：20918-20922
DOI：10.1073/pnas.1117152108
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Stishovite (SiO2 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 {degrees}C near 10 GPa produces stishovite with significant amounts of H2O 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 % H2O and NMR suggests that the primary mechanism for the H2O uptake is a direct hydrogarnet-like substitution of 4H+ for Si4+, with the protons clustered as hydroxyls around a silicon vacancy. This substitution is accompanied by a substantial volume decrease for the system (SiO2 + H2O), although the stishovite expands slightly, and it is only slightly unfavorable in energy. Stishovite could thus be a host for H2O at convergent plate boundaries, and in other relatively cool high-pressure environments.
