Abstract
Pyroxene is an important carrier of ferric iron in basalt and the upper mantle. Understanding the influence of pyroxene crystallization on the oxygen fugacity of magma relies on accurate knowledge of the oxidation state of iron, expressed as the Fe3+/ΣFe ratio, in pyroxene. To accurately determine the Fe3+/ΣFe ratio in pyroxene using electron probe microanalysis, we present nine natural pyroxene samples, including one aegirine, one hedenbergite, one diopside, and six augites, for the calibration of the flank method for pyroxene. The aegirine sample is rich in the aegirine end-member with a Fe3+/ΣFe ratio of 0.98 ± 0.01 (1σ), while the hedenbergite sample is rich in the hedenbergite end-member and free of ferric iron. The augite and diopside samples contain variable ferric iron, with the Fe3+/ΣFe ratios varying from 0.21 to 0.39. Based on the flank positions of FeLα and FeLβ determined by natural andradite and almandine, we measured the Fe Lβ/Lα ratios at the flank positions for the pyroxene samples. The results demonstrate a positive linear relationship between the Fe Lβ/Lα ratios and the Fe2+ content of the pyroxene samples. The Fe2+ contents and Fe3+/ΣFe ratios of the pyroxene samples, as determined through a multiple linear regression equation, align closely with those obtained by Mössbauer spectroscopy. This method yields the Fe2+ content and Fe3+/ΣFe ratios with an error of ±0.3 wt% and ±0.06, respectively, for calcic pyroxene containing 7 wt% total FeO. These well-characterized natural pyroxene samples can serve as reference materials for determining the Fe3+/ΣFe ratio in unknown calcic pyroxene.
Acknowledgments and Funding
We thank Jintuan Wang for his assistance with sample preparation; Xiaoju Lin for helping with Raman analysis; Qiuxia Wang for helping with Mössbauer analysis. We also thank Pengli He for providing the clinopyroxene reference material to be used as the secondary standard. We appreciate John Fournelle and Stuart Kearns for constructive comments and Don Baker for efficient editorial handling. This study was financially supported by the National Key R&D Program of China (2018YFA0702600) and the Science and Technology Planning Project of Guangdong Province, China (2023B1212060048).
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Articles in the same Issue
- Hematite (U-Th)/He thermochronometry unveils unique exhumation history: An example from the Dexing porphyry copper deposit, Southern China
- Viscosity measurements of selected lunar regolith simulants
- Formation of nano-CdS solid solution: A mechanism for Cd enrichment in sphalerite
- Identification of the nature of recycled carbonates in the mantle: Insights from the Mo-Mg isotopic pair
- Discriminating ionic mobility between diffusivity and electrical conductivity experiments on Earth’s silicate materials
- Morphological approach to understanding mineral alteration and nanoparticle formation under alkaline conditions using granitic rock thin sections
- Identification of hydroandradite in CM carbonaceous chondrites: Aproduct of calc-silicate alteration on C-complex asteroids
- Growth and crystallographic features of interpenetrant twins in natural diamonds
- Determination of the oxidation state of iron in calcic pyroxene using the electron microprobe flank method
- Formation mechanism of boehmite and diaspore in karstic bauxites: Trace element geochemistry in source materials using a large sample geochemical dataset and a random forest model
- High-temperature Raman spectroscopy of K2Ca(CO3)2 bütschliite and Na2Ca2(CO3)3 shortite
- Effects of high-temperature annealing and low-temperature metamictization on Archean zircon: Constraints from U-Pb isotopes, trace elements, and Raman dating
- Nanoscale insights into weathering of Ti-bearing minerals and heterogeneous crystal growth mechanisms of nano Ti oxides in altered volcanic ash
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