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American Mineralogist

Journal of Earth and Planetary Materials

Ed. by Baker, Don / Xu, Hongwu / Swainson, Ian


IMPACT FACTOR 2018: 2.631

CiteScore 2018: 2.55

SCImago Journal Rank (SJR) 2018: 1.355
Source Normalized Impact per Paper (SNIP) 2018: 1.103

Online
ISSN
1945-3027
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Volume 100, Issue 5-6

Issues

Quantification of water in majoritic garnet

Sylvia-Monique Thomas / Kathryn Wilson / Monika Koch-Müller / Erik H. Hauri
  • Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, D.C. 20015, U.S.A.
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/ Catherine McCammon / Steven D. Jacobsen
  • Department of Earth and Planetary Sciences, Northwestern University, Evanston, Illinois 60208, U.S.A.
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/ John Lazarz
  • Department of Earth and Planetary Sciences, Northwestern University, Evanston, Illinois 60208, U.S.A.
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/ Dieter Rhede / Minghua Ren / Neal Blair
  • Department of Earth and Planetary Sciences, Northwestern University, Evanston, Illinois 60208, U.S.A.
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/ Stephan Lenz
Published Online: 2015-05-12 | DOI: https://doi.org/10.2138/am-2015-5136

Abstract

Majoritic garnet, characterized by an excess of silicon (>3 Si per formula unit), is considered one of the major phases of the Earth’s transition zone from 410-660 km depth. Quantifying the H2O content of nominally anhydrous mantle minerals is necessary to evaluate their water storage capacity from experiments and modeling the Earth’s deep water cycle. We present mineral-specific infrared absorption coefficients for the purpose of quantifying the amount of water incorporated into majorite as hydroxyl point defects. A suite of majoritic garnet samples with varying proportions of Si, Fe, Al, Cr, and H2O was synthesized at conditions of 18-19 GPa and 1500-1800 °C. Single-crystals were characterized using X‑ray diffraction, electron microprobe analysis, secondary ion mass spectrometry (SIMS), IR, Raman, and Mössbauer spectroscopy. We utilize SIMS and Raman spectroscopy in combination with IR spectroscopy to provide IR absorption coefficients for water in majoritic garnets with the general mineral formula (Mg,Fe)3(Si,Mg,Fe,Al,Cr)2[SiO4]3. The IR absorption coefficient for majoritic garnet in the OH stretching region is frequency dependent and ranges from 10 470 ± 3100 Lmol-1cm-2 to 23 400 ± 2300 Lmol-1cm-2.

Keywords: IR spectroscopy; water in nominally anhydrous minerals; transition zone; integral molar absorption coefficient; SIMS; high pressure; Raman spectroscopy

About the article

Received: 2014-07-21

Accepted: 2014-12-15

Published Online: 2015-05-12

Published in Print: 2015-05-01


Citation Information: American Mineralogist, Volume 100, Issue 5-6, Pages 1084–1092, ISSN (Online) 1945-3027, ISSN (Print) 0003-004X, DOI: https://doi.org/10.2138/am-2015-5136.

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© 2015 by Walter de Gruyter Berlin/Boston.

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