IR calibrations for water determination in olivine, r-GeO2, and SiO2 polymorphs

Thomas, Steven; Koch‐Müller, Monika; Reichart, P.; Rhede, Dieter; Thomas, Rainer; Wirth, Richard; Matsyuk, S. S.

doi:10.1007/s00269-009-0295-1

Cited by 88 publications

(104 citation statements)

References 71 publications

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“…We regard the calibration curve of Libowitzky and Rossman (1997) as most reliable because the curve is based on direct measurements of many samples. However, it has been observed that the general trend of increasing ε with decreasing wavenumber is valid only for hydrous minerals and glasses and should not be applied to water quantification in nominally anhydrous minerals (NAMs), which incorporate traces of water in their structures (e.g., Rossman 2006;Thomas et al 2009). For example, Bell et al (2003) showed that if the general IR calibration of Paterson (1982) is adopted, the water concentration of olivine is underestimated by about 25%.…”

Section: Introductionmentioning

confidence: 99%

IR absorption coefficients for water in nominally anhydrous high-pressure minerals

Koch‐Müller

Rhede

2010

American Mineralogist

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Infrared spectroscopic quantification of traces of OH and H 2 O in minerals and glasses is based on the Beer Lambert law A = ε·c·t, where ε is the molar absorption coefficient. Numerous experimental and theoretical studies show that ε generally increases with decreasing wavenumbers. However, this general trend seems to be valid only for hydrous minerals and glasses and should not be applied to water quantification in nominally anhydrous minerals (NAMs) that incorporate traces of water in their structures. In this study, we analyze ε-values from literature data and propose that within a polymorphic mineral series of the same composition ε negatively correlates with the molar volume and positively correlates with the density of the respective mineral phase. To test this hypothesis, we determined ε-values for synthetic hydrous ringwoodite samples ranging in composition from X Mg = 0.0 to 0.6 by combining results of FTIR-spectroscopy with those of secondary ion mass spectrometry. The ε-values plot well below the general calibration curves but follow the same trend, i.e., they increase with decreasing wavenumbers of the OH bands from 59 000 ± 6000 for the Fe end-member to 85 800 ± 10 000 L/mol(H 2 O)/cm -2 for the Mg-richest sample. From this relation we can predict an absorption coefficient for the iron-free Mg end-member as 100 000 ± 7000 L/mol(H 2 O)/cm -2 . This value together with ε-values for forsterite and wadsleyite taken from literature confirm the proposed correlation with the molar volume and density within this polymorphic series. This allows us to predict absorption coefficients for some minerals, where coefficients for one or better two of their polymorphs, either high-or low-pressure, are available.

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Section: Introductionmentioning

confidence: 99%

IR absorption coefficients for water in nominally anhydrous high-pressure minerals

Koch‐Müller

Rhede

2010

American Mineralogist

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“…To the extent that spectra include sharp OH absorption bands due to hydrogen point defects, this calibration will overesti-mate OH concentrations due to H interstitials, given that the value of k for these bands is larger than for molecular water (Kats, 1962;Thomas et al, 2009) for quartz grains oriented for maximum OH absorbance (vibrational directions perpendicular to the c axis). However, apparent OH concentrations due to H interstitials will appear smaller for quartz grains oriented for minimum OH absorbance in unpolarized IR radiation.…”

Section: Ir Plate Thickness and Oh Absorbance Determinationsmentioning

confidence: 99%

“…The variations in size of sharp OH bands associated with hydrogen point defects, by comparison, are much smaller. The sizes of these absorption bands may be explained by differing quartz grain orientations without calling upon any variations in hydrogen point defect concentrations (Thomas et al, 2009). …”

Section: Synchrotron Ftir Measurementsmentioning

confidence: 99%

Synchrotron FTIR imaging of OH in quartz mylonites

et al. 2017

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Abstract. Previous measurements of water in deformed quartzites using conventional Fourier transform infrared spectroscopy (FTIR) instruments have shown that water contents of larger grains vary from one grain to another. However, the non-equilibrium variations in water content between neighboring grains and within quartz grains cannot be interrogated further without greater measurement resolution, nor can water contents be measured in finely recrystallized grains without including absorption bands due to fluid inclusions, films, and secondary minerals at grain boundaries.Synchrotron infrared (IR) radiation coupled to a FTIR spectrometer has allowed us to distinguish and measure OH bands due to fluid inclusions, hydrogen point defects, and secondary hydrous mineral inclusions through an aperture of 10 µm for specimens > 40 µm thick. Doubly polished infrared (IR) plates can be prepared with thicknesses down to 4-8 µm, but measurement of small OH bands is currently limited by strong interference fringes for samples < 25 µm thick, precluding measurements of water within individual, finely recrystallized grains. By translating specimens under the 10 µm IR beam by steps of 10 to 50 µm, using a software-controlled x − y stage, spectra have been collected over specimen areas of nearly 4.5 mm 2 . This technique allowed us to separate and quantify broad OH bands due to fluid inclusions in quartz and OH bands due to micas and map their distributions in quartzites from the Moine Thrust (Scotland) and Main Central Thrust (Himalayas).Mylonitic quartzites deformed under greenschist facies conditions in the footwall to the Moine Thrust (MT) exhibit a large and variable 3400 cm −1 OH absorption band due to molecular water, and maps of water content corresponding to fluid inclusions show that inclusion densities correlate with deformation and recrystallization microstructures. Quartz grains of mylonitic orthogneisses and paragneisses deformed under amphibolite conditions in the hanging wall to the Main Central Thrust (MCT) exhibit smaller broad OH bands, and spectra are dominated by sharp bands at 3595 to 3379 cm −1 due to hydrogen point defects that appear to have uniform, equilibrium concentrations in the driest samples. The broad OH band at 3400 cm −1 in these rocks is much less common. The variable water concentrations of MT quartzites and lack of detectable water in highly sheared MCT mylonites challenge our understanding of quartz rheology. However, where water absorption bands can be detected and compared with deformation microstructures, OH concentration maps provide information on the histories of deformation and recovery, evidence for the introduction and loss of fluid inclusions, and water weakening processes.

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“…Water concentrations were calculated by integrating the polarized background-corrected IR spectra (normalized to thickness) across the region of absorption due to OH dipole vibrations (3700-3200 cm −1 ). The integrated extinction coefficients from mineral-specific Thomas et al 2009) and general wavelength-specific (Libowitzky and Rossman 1997) calibrations were used. All three calibrations yield for most samples results in excellent agreement to each other.…”

Section: Ftir Spectroscopymentioning

confidence: 99%