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Published May 1995 | public
Journal Article

Quantitative analysis of trace OH in garnet and pyroxenes

Abstract

To calibrate infrared (IR) spectroscopy for quantitative analysis of trace structural OH in specific minerals, we have determined concentrations of H in pure separates of mantle derived pyrope garnet (56 ± 6 ppm H_2O by weight), augite (268 ± 8, ppm H_2O, and enstatite (217 ± 11 ppm H_2O) by manometry after heating the samples and extracting H_2 gas under vacuum. IR spectroscopy confirmed the presence of intrinsic OH in these samples prior to extraction and indicated between 86 and 100% removal of H during the extraction procedure. The integral specific absorption coefficients of 1.39 ± 0.14(lσ),7.09 ± 0.32, and 15.6 ± 0.94 /(ppm H_2O.cm^2) for pyrope, augite, and enstatite, respectively, allow precise spectroscopic determination of the OH content of upper mantle garnets and pyroxenes to concentration levels of a few parts per million. Uncertainties in accuracy depend on mineral composition and characteristics of the OH absorption spectrum and are estimated to range between ± 10 and ± 50%.

Additional Information

© 1995 Mineralogical Society of America. Manuscript received June8, 1994. Manuscript accepted February 9, 1995. This research was funded by NSF grants EAR-8816006 and EAR- 9104059 to G.R.R. and DOE grant DE-FG03-58ER13445 to Samuel Epstein. We are grateful to S. Epstein for access to his analytical facilities and the accompanying know-how. D.R.B. thanks Patrick Bartlett, Glen Mattioli, Rory Moore, and Moti Stein for help with acquisition of these rare samples and De Beers Consolidated Mines and Sydney Gasson for access to the Premier and Monastery Mines, respectively. We thank Ed Stolper for encouragement and helpful suggestions and M.D. Dyar, T.C. Hoering, and A.M. Hofmeister for reviews. This work is contribution number 5379, Division of Geological and Planetary Sciences, California Institute of Technology.

Additional details

Created:
August 22, 2023
Modified:
October 26, 2023