A composition-independent quantitative determination of the water content in silicate glasses and silicate melt inclusions by confocal Raman spectroscopy (original) (raw)
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Geochimica Et Cosmochimica Acta, 2009
The development of an accurate analytical procedure for determination of dissolved water in complex alumino-silicate glasses via micro-Raman analysis requires the assessment of the spectra topology dependence on glass composition. We report here a detailed study of the respective influence of bulk composition, iron oxidation state and total water content on the absolute and relative intensities of the main Raman bands related to glass network vibrations (LF: ~490 cm −1 ; HF: ~960 cm −1 ) and total water stretching (H 2 O T : ~3550 cm −1 ) in natural glasses. The evolution of spectra topology was examined in (i) 33 anhydrous glasses produced by the re-melting of natural rock samples, which span a very large range of polymerisation degree (NBO/T from 0.00 to 1.16), (ii) 2 sets of synthetic anhydrous basaltic glasses with variable iron oxidation state (Fe 3+ /Fe T from 0.05 to 0.87), and (iii) 6 sets of natural hydrous glasses (C H2OT from 0.4 to 7.0 wt%) with NBO/T varying from 0.01 to 0.76.
Journal of Raman Spectroscopy, 2019
The physical properties of silicate melts are of critical importance for understanding magmatic and volcanic processes on Earth and other planets. Most physical properties of melts are, ultimately, a consequence of the structural organization of the melt. Robust and fully generalizable strategies for the prediction of properties of naturally occurring melts as functions of composition, temperature, and pressure remain a challenging goal. Given the structural origin of macroscopic properties, Raman spectroscopy of glasses, which provides information on melt and glass structure, may provide a useful technique to understanding and quantify variations in macroscopic melt properties. Here, with the aim of providing a generalizable model for predicting the viscosity of silicate melts, we present the results of a Raman spectroscopy campaign performed on 30 anhydrous multicomponent silicate glasses resulting from quenching of remelted and homogenized volcanic rocks and synthetic equivalents...
Applied Geochemistry, 2006
Development of Raman spectrometry for quantification of water content in natural glasses requires the assessment of the dependence of the technique on glass composition and thermal history. In the low frequency domain, Raman spectra topology varies due to glass depolymerization and substitution in the framework of (Si 4+ ) IV by alkali-balanced (Al 3+ ) IV and (Fe 3+ ) IV in calcalkaline (rhyolite to basaltic andesite) and alkaline (trachyte, phonolite to alkali basalt) glasses. These processes result in strong dependence of previous analytical procedure (internal calibration) on glass composition. Here, we show that an analytical procedure based on calibration to an external standard is only faintly composition-dependent for Si-rich alkaline glasses (trachytes-phonolites). For a given glass composition, thermal history also plays a fundamental role in the choice of Raman procedure for water analysis. Repeated cycles of thermal annealing induce microcrystallization of hydrous trachyte glasses and modify cation distribution in the glass structure. Application of these concepts to analysis of banded obsidians suggests that small-scale heterogeneities in glasses are not simply related to magma degassing, but could depend on thermal history and consequent relaxation paths in the melt.
Laser Raman spectroscopic measurements of water in unexposed glass inclusions
American Mineralogist, 2006
A method is proposed for determining the water concentration in silicate melt inclusions (MI) by confocal micro-Raman spectroscopy, without exposing the inclusions for measurement (a prerequisite of all previous methods). The latter is important for extremely water-rich MI (e.g., those in evolved granites and pegmatites), which would loose H 2 O on exposure. Furthermore, this technique permits determination of the water concentration in a single MI. We use a comparative technique, determining the total water content of a sample against a reference glass of known water content. Because this process is non-destructive it does not preclude the subsequent use of other analytical techniques.
The determination of total water content (H 2 O T : 0.1-10 wt%) and water speciation (H 2 O molecular /OH) in volcanic products by confocal microRaman spectrometry are discussed for alkaline (phonolite) and calcalkaline (dacite and rhyolite) silicic glasses. Shape and spectral distribution of the total water band (H 2 O T ) at 3550 cm −1 show systematic evolution with glass H 2 O T , water speciation and NBO/T. In the studied set of silicic samples, calibrations based on internal normalization of the H 2 O T band to a band related to vibration of aluminosilicate network (TOT) at 490 cm −1 vary with glass peraluminosity. An external calibration procedure using well-characterized glass standards is less composition-dependent and provides excellent linear correlation between total dissolved water content and height or area of the H 2 O T Raman band. Accuracy of deconvolution procedure of the H 2 O T band to quantify water speciation in water-rich and depolymerized glasses depends on the strength of OH hydrogen bonding. System confocal performance, scattering from embedding medium and glass microcrystallinity have a crucial influence on accuracy of Raman analyses of water content in glass-bearing rocks and melt inclusions in crystals.
American Mineralogist
We tested our calibration on several silicate glasses equilibrated under moderately reducing conditions (QFM+0.8 ≤ fO2 ≤ QFM+1.4) in which S is dissolved as both SO4 2and S 2-. We also analysed several olivine-hosted melt inclusions collected from Etna and for which the fO2 and S speciation is unknown. For these samples, the S content estimated by the Raman calibration is systematically lower than the total S measured by EPMA. We combined both methods to estimate the S 2content not accounted for by Raman and derive the S speciation and fO2 conditions. The derived fO2 is consistent with the imposed fO2 for synthesised glasses and with current assumed fO2 conditions for basaltic melt inclusions from Etna.
Spectroscopic analysis (FTIR, Raman) of water in mafic and intermediate glasses and glass inclusions
Geochimica Et Cosmochimica Acta, 2010
Micro-Raman spectroscopy, even though a very promising technique, is not still routinely applied to analyse H 2 O in silicate glasses. The accuracy of Raman water determinations critically depends on the capability to predict and take into account both the matrix effects (bulk glass composition) and the analytical conditions on band intensities. On the other hand, micro-Fourier transform infrared spectroscopy is commonly used to measure the hydrous absorbing species (e.g., hydroxyl OH À and molecular H 2 O) in natural glasses, but requires critical assumptions for the study of crystal-hosted glasses. Here, we quantify for the first time the matrix effect of Raman external calibration procedures for the quantification of the total H 2 O content (H 2 O T = OH À + H 2 O m ) in natural silicate glasses. The procedures are based on the calibration of either the absolute (external calibration) or scaled (parameterisation) intensity of the 3550 cm À1 band. A total of 67 mafic (basanite, basalt) and intermediate (andesite) glasses hosted in olivines, having between 0.2 and 4.8 wt% of H 2 O, was analysed. Our new dataset demonstrates, for given water content, the height (intensity) of Raman H 2 O T band depends on glass density, reflectance and water environment. Hence this matrix effect must be considered in the quantification of H 2 O by Raman spectroscopy irrespective of the procedure, whereas the parameterisation mainly helps to predict and verify the self-consistency of the Raman results. In addition, to validate the capability of the micro-Raman to accurately determine the H 2 O content of multicomponent aluminosilicate glasses, a subset of 23 glasses was analysed by both micro-Raman and micro-FTIR spectroscopy using the band at 3550 cm À1 . We provide new FTIR absorptivity coefficients (e 3550 ) for basalt (62.80 ± 0.8 L mol À1 cm À1 ) and basanite (43.96 ± 0.6 L mol À1 cm À1 ). These values, together with an exhaustive review of literature data, confirm the non-linear decline of the FTIR absorptivity coefficient (e 3550 ) as the glass depolymerisation increases. We demonstrate the good agreement between micro-FTIR and micro-Raman determination of H 2 O in silicate glasses when the matrix effects are properly considered.
Approximate chemical analysis of volcanic glasses using Raman spectroscopy
Journal of Raman Spectroscopy, 2015
The effect of chemical composition on the Raman spectra of a series of natural calcalkaline silicate glasses has been quantified by performing electron microprobe analyses and obtaining Raman spectra on glassy filaments (~450 μm) derived from a magma mingling experiment. The results provide a robust compositionally-dependent database for the Raman spectra of natural silicate glasses along the calcalkaline series. An empirical model based on both the acquired Raman spectra and an ideal mixing equation between calcalkaline basaltic and rhyolitic end-members is constructed enabling the estimation of the chemical composition and degree of polymerization of silicate glasses using Raman spectra. The model is relatively insensitive to acquisition conditions and has been validated using the MPI-DING geochemical standard glasses as well as further samples. The methods and model developed here offer several advantages compared with other analytical and spectroscopic methods such as infrared spectroscopy, X-ray fluorescence spectroscopy, electron and ion microprobe analyses, inasmuch as Raman spectroscopy can be performed with a high spatial resolution (1 μm 2 ) without the need for any sample preparation as a nondestructive technique. This study represents an advance in efforts to provide the first database of Raman spectra for natural silicate glasses and yields a new approach for the treatment of Raman spectra, which allows us to extract approximate information about the chemical composition of natural silicate glasses using Raman spectroscopy. We anticipate its application in handheld in situ terrestrial field studies of silicate glasses under extreme conditions (e.g. extraterrestrial and submarine environments).