• journal_title：Mineralogical Magazine
• Contributor：M. Fialin ; C. Wagner ; M.-L. Pascal
• Publisher：Mineralogical Society of Great Britain and Ireland
• Date：2011-
• Format：text/html
• Language：en
• Identifier：10.1180/minmag.2011.075.2.347
• journal_abbrev：Mineralogical Magazine
• issn：0026-461X
• volume：75
• issue：2
• firstpage：347
• section：Articles

A quantitative determination of Fe<sup>3+sup>/ΣFe ratios using the electron microprobe is presented for glasses. The measurements are based on the shift of the Fe-Lα peak position between Fe<sup>3+sup> and Fe<sup>2+sup>, resulting from differences in self-absorption. We present new calibration curves for glasses with Fe contents as low as 2 wt.% Fe.

This method was used for glasses from a metasomatized spinel lherzolite (Massif Central, France) in which highly vesicular glass associated with secondary minerals occurs in reaction pockets around corroded Cr-spinels. The glass was found to be oxidized homogeneously with Fe<sup>3+sup>/ΣFe ≈ 0.70 (measured with an uncertainty of ±0.06), in contrast with the value of ∼0.15 that would correspond to the former melt under f<sub>O<sub>2sub>sub> conditions inferred from secondary minerals. The glass oxidation probably results from the dissociation of the melt-water content under degassing, prior to local hematite depositions (spinel rims and crack fillings).