Infrared spectra of high-pressure hydrous silicates in the system MgO-SiO2-H2O |
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| Authors: | Masaki Akaogi Syun-iti Akimoto |
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| Institution: | 1. Department of Earth Sciences, Kanazawa University, Marunouchi, 920, Kanazawa, Japan
2. Institute for Solid State Physics, University of Tokyo, Roppongi, Minato-ku, 106, Tokyo, Japan
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| Abstract: | Infrared absorption spectra are presented for four hydrous magnesian silicates which are stable at high pressures and high temperatures characteristic of the earth's mantle: phase A (Mg7Si2O14H6), phase B (approx. Mg23Si8O42H6), chondrodite (Mg5Si2O10H2), clinohumite (Mg9Si4O18H2). The results show that phase B as well as phase A, chondrodite and clinohumite contain hydroxyl groups in their structures. It is also suggested that phase B, in addition to phase A, could be of potential importance in the upper mantle and transition zone as a dense host mineral for hydroxyl ions. Chemical composition of phase A was reexamined by microprobe analysis: it agrees well with Mg7Si2O14H6, estimated by Yamamoto and Akimoto (1974, 1977), but disagrees with a newly proposed formula Mg2SiO5H2 by Benimoff and Sclar (1984). |
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