Crystal structures of quartz and stishovite. Quartz consists of silicon-oxygen tetrahedrons (SiO4), while stishovite consists of silicon-oxygen octahedrons (SiO6). Quartz possesses 4-coordinate silicon, a typical silicate structure found in the upper mantle, whereas stishovite possesses 6-coordinated silicon, a typical silicate structure found in the lower mantle. In this study, it was found that muoniums exist not only in quartz but also in the small and anisotropic interstitial voids (white areas) in stishovite.
Credit: Image courtesy of National Institute for Materials Science (NIMS)
A research group led by Associate Professor Nobumasa Funamori, Department of Earth and Planetary Science, Graduate School of Science, University of Tokyo, along with research groups specialized in high-pressure Earth science and muon science, including the Institute of Materials Structure Science, jointly studied the condition of muons (µ+, mu particles) implanted in stishovite, a high-pressure phase of quartz, using the muon spin rotation method, and found that muons exist in interstitial positions in the form of muoniums with a captured electron.
A muon is a particle that mimics the condition of a proton (H+) in materials as a light radioisotope of proton. Because muonium (µ0) corresponds to neutral atomic hydrogen (H0), experimental results suggest the possible existence of neutral atomic hydrogen in interstitial positions in stishovite.
This finding challenges the established dogma that hydrogen exists in the form of a hydroxyl group (i.e., water) in silicate minerals that make up rocks, and is expected to open up new possibilities for identifying the mechanism behind the hydrogen cycle in the Earth’s deep interior.
In addition to the Graduate School of Science of the University of Tokyo and the Institute of Materials Structure Science, Hiroshima University, National Institute for Materials Science, Ehime University and RIKEN contributed to this study.
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- Nobumasa Funamori, Kenji M. Kojima, Daisuke Wakabayashi, Tomoko Sato, Takashi Taniguchi, Norimasa Nishiyama, Tetsuo Irifune, Dai Tomono, Teiichiro Matsuzaki, Masanori Miyazaki, Masatoshi Hiraishi, Akihiro Koda, Ryosuke Kadono. Muonium in Stishovite: Implications for the Possible Existence of Neutral Atomic Hydrogen in the Earth's Deep Mantle. Scientific Reports, 2015; 5: 8437 DOI: 10.1038/srep08437
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National Institute for Materials Science (NIMS). "Possible existence of neutral atomic hydrogen in rock in Earth's deep interior." ScienceDaily. ScienceDaily, 25 March 2015. <www.sciencedaily.com/releases/2015/03/150325082343.htm>.
National Institute for Materials Science (NIMS). (2015, March 25). Possible existence of neutral atomic hydrogen in rock in Earth's deep interior. ScienceDaily. Retrieved May 27, 2017 from www.sciencedaily.com/releases/2015/03/150325082343.htm
National Institute for Materials Science (NIMS). "Possible existence of neutral atomic hydrogen in rock in Earth's deep interior." ScienceDaily. www.sciencedaily.com/releases/2015/03/150325082343.htm (accessed May 27, 2017).