Ultrahydrous stishovite from high-pressure hydrothermal treatment of SiO(2)
2011 (English)In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 108, no 52, 20918-20922 p.Article in journal (Refereed) Published
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 degrees C near 10 GPa produces stishovite with significant amounts of H(2)O 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(2)O and NMR suggests that the primary mechanism for the H(2)O 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(2)O), although the stishovite expands slightly, and it is only slightly unfavorable in energy. Stishovite could thus be a host for H(2)O at convergent plate boundaries, and in other relatively cool high-pressure environments.
Place, publisher, year, edition, pages
2011. Vol. 108, no 52, 20918-20922 p.
low temperature, high-pressure synthesis, hydrothermal environments, multianvil technique
IdentifiersURN: urn:nbn:se:su:diva-71151DOI: 10.1073/pnas.1117152108ISI: 000298479900018OAI: oai:DiVA.org:su-71151DiVA: diva2:483920
authorCount :82012-01-262012-01-262012-01-26Bibliographically approved