Structural systematics of hydrous ringwoodite and water in Earth's interior

Joseph R. Smyth*, Christopher M. Holl, Daniel J. Frost, Steven D. Jacobsen, Falko Langenhorst, Catherine A. Mccammon

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

106 Scopus citations

Abstract

Seven separate samples of hydrous ringwoodite with compositions ranging from Fo100 to Fo89 and hydrogen contents from 0.2 to 1.1 wt% were synthesized in the 5000 ton multi-anvil press at the Bayerisches Geoinstitut. Synthesis conditions ranged from 18 to 22 GPa and 1400 to 1500 °C. The crystals were characterized by single-crystal X-ray diffraction, electron microprobe, IR and Mössbauer spectroscopy, and by analytical and high-resolution transmission electron microscopy. The crystals are optically isotropic, and the Fe-bearing samples are deep blue in color. Mössbauer spectroscopy and ELNE spectroscopy applied to the Fe-bearing samples indicates about 10% of the iron is in the ferric state. High-resolution TEM examination of one of the Fe-bearing samples indicates that the crystals are homogeneous and free of significant inclusions or exsolution features. Infrared spectra show a broad absorption band extending from about 2500 to 3600 cm 1 with maxima ranging from 3105 for the pure magnesian samples to 3150 cm-1 for the Fo89 samples. The crystal structures of the seven ringwoodite samples were refined by X-ray single-crystal diffraction. Refinement of cation site occupancies indicates full occupancy of the tetrahedral site for all samples, whereas the occupancy of the octahedral site appears to decrease systematically with H content. The principal hydration mechanism involves octahedral cation vacancies. The IR spectra are consistent with protonation of the short O-O approach on the tetrahedral edge, which would imply partial Mg-Si disorder.

Original languageEnglish (US)
Pages (from-to)1402-1407
Number of pages6
JournalAmerican Mineralogist
Volume88
Issue number10
DOIs
StatePublished - Oct 2003

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology

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