Determination of ferrous-ferric iron contents in tourmaline using synchrotron-based XANES

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Marco E. Ciriotti
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Iscritto il: ven 25 giu, 2004 11:31
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Determination of ferrous-ferric iron contents in tourmaline using synchrotron-based XANES

Messaggio da Marco E. Ciriotti » ven 20 lug, 2018 9:55

Referenza:
▪ Levy, E.A., Henry, D.J., Roy, A., Dutrow, B.L. (2018): Determination of ferrous-ferric iron contents in tourmaline using synchrotron-based XANES. Journal of Geosciences, 63, 167-174.

Abstract:
The complex geochemistry of tourmaline makes it an important tool in determining its formational environment. Typically, tourmaline chemistry is analyzed through electron-probe microanalysis (EPMA), but this analytical tool cannot determine directly the oxidation states of transition elements such as Fe (Fe2+, Fe3+). Direct quantitative measurement of these cations is important in minerals to acquire a more complete chemical characterization and informative structural formula. Synchrotron-based X-ray Absorption Near Edge Spectroscopy (XANES) is a method to directly measure Fe2+ and Fe3+ in minerals, including tourmaline. This method utilizes advances in software and detector technology to significantly decrease data processing time and errors.
Three tourmaline samples, dravite, povondraite, and oxy-schorl, analyzed by combining XANES and EPMA data, exhibit distinct ferrous-ferric contents using the pre-edge and absorption edge methods. These analyses reveal, respectively: 99.62-100 wt. % Fe2+ in dravite, 12.5-20.00 wt. % Fe2+ vs. 87.48-100 wt. % Fe3+ in povondraite, and 63.03wt. % Fe2+ vs. 36.98-36.41 wt. % Fe3+ in schorl. Information on the oxidation states of Fe results in enhanced charge-balanced constraints that allow improved estimation of the H contents in the tourmaline and a more accurate designation of the structural formula and classification of tourmaline species. Thus, XANES is a viable technique to obtain oxidation states of transition elements in tourmaline.
Marco E. Ciriotti

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