Microanalysis of the iron oxidation state in (Mg,Fe)O and application to the study of microscale processes

Micaela Longo; Catherine A. McCammon; Steven D. Jacobsen

doi:10.1007/s00410-011-0649-9

Microanalysis of the iron oxidation state in (Mg,Fe)O and application to the study of microscale processes

Micaela Longo^*, Catherine A. McCammon, Steven D. Jacobsen

^*Corresponding author for this work

Earth, Environmental, and Planetary Sciences

Research output: Contribution to journal › Article › peer-review

23 Scopus citations

Abstract

We report application of the flank method using the electron microprobe to a suite of twelve (Mg,Fe)O samples with composition 2-47 wt% Fe and Fe³⁺/ΣFe=1 to 11%, where Fe³⁺/ΣFe was determined independently using Mössbauer spectroscopy on the same grains used for the flank method measurements. A calibration curve of the form Fe²⁺=A+B× (ΣFe)²+C× (Lβ/Lα) was fit to the data and gave excellent agreement between Fe³⁺/ΣFe calculated from the flank method and Fe³⁺/ΣFe determined using Mössbauer spectroscopy. We found the method to be sufficiently sensitive to determine meaningful variations in Fe³⁺/ΣFe for geophysically relevant compositions of (Mg,Fe)O (<25 wt% Fe), and calibration parameters remained constant within experimental uncertainty over the course of the entire study (20 months). Flank method measurements on an inhomogeneous sample of synthetic (Mg,Fe)O showed evidence of diffusion processes resulting from rupture of the capsule during the high-pressure experiment and the possibility to measure Lβ/Lα variations with a spatial resolution of a few microns. We detected the presence of exsolved magnesioferrite in a suite of (Mg,Fe)O single crystals using transmission electron microscopy and Mössbauer spectroscopy. Flank method measurements on the same suite of single crystals showed enhanced Fe³⁺/ΣFe values, consistent with the presence of magnesioferrite even though the grains were too small to be resolved by conventional electron microprobe measurements.

Original language	English (US)
Pages (from-to)	1249-1257
Number of pages	9
Journal	Contributions to Mineralogy and Petrology
Volume	162
Issue number	6
DOIs	https://doi.org/10.1007/s00410-011-0649-9
State	Published - Dec 2011

Funding

Acknowledgments We are grateful to Stephen Mackwell for supplying some of the samples examined in this study, to Hugh O’Neill for valuable advice concerning (Mg,Fe)O synthesis, to Heidi Höfer for her support on the flank method calibration, to Detlef Krauße for his technical support at the electron microprobe, to Nobuyoshi Mi-yajima for TEM investigations and to Florian Heidelbach for SEM analyses. The manuscript was significantly improved by the comments of Andrew Berry and an anonymous reviewer. ML received financial support from the European Commission under the Marie Curie Action for Early Stage Training of Researchers within the 6th Framework Programme (contract number MEST-CT-2005-019700). SDJ is supported in part by the US NSF (EAR-0748707) and by the David and Lucile Packard Foundation.

Keywords

Electron microprobe
Ferropericlase
Flank method
Iron oxidation state

ASJC Scopus subject areas

Geophysics
Geochemistry and Petrology

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10.1007/s00410-011-0649-9

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@article{8a29248fbc59459db592ba610315fc2b,

title = "Microanalysis of the iron oxidation state in (Mg,Fe)O and application to the study of microscale processes",

abstract = "We report application of the flank method using the electron microprobe to a suite of twelve (Mg,Fe)O samples with composition 2-47 wt% Fe and Fe3+/ΣFe=1 to 11%, where Fe3+/ΣFe was determined independently using M{\"o}ssbauer spectroscopy on the same grains used for the flank method measurements. A calibration curve of the form Fe2+=A+B× (ΣFe)2+C× (Lβ/Lα) was fit to the data and gave excellent agreement between Fe3+/ΣFe calculated from the flank method and Fe3+/ΣFe determined using M{\"o}ssbauer spectroscopy. We found the method to be sufficiently sensitive to determine meaningful variations in Fe3+/ΣFe for geophysically relevant compositions of (Mg,Fe)O (<25 wt% Fe), and calibration parameters remained constant within experimental uncertainty over the course of the entire study (20 months). Flank method measurements on an inhomogeneous sample of synthetic (Mg,Fe)O showed evidence of diffusion processes resulting from rupture of the capsule during the high-pressure experiment and the possibility to measure Lβ/Lα variations with a spatial resolution of a few microns. We detected the presence of exsolved magnesioferrite in a suite of (Mg,Fe)O single crystals using transmission electron microscopy and M{\"o}ssbauer spectroscopy. Flank method measurements on the same suite of single crystals showed enhanced Fe3+/ΣFe values, consistent with the presence of magnesioferrite even though the grains were too small to be resolved by conventional electron microprobe measurements.",

keywords = "Electron microprobe, Ferropericlase, Flank method, Iron oxidation state",

author = "Micaela Longo and McCammon, {Catherine A.} and Jacobsen, {Steven D.}",

note = "Funding Information: Acknowledgments We are grateful to Stephen Mackwell for supplying some of the samples examined in this study, to Hugh O{\textquoteright}Neill for valuable advice concerning (Mg,Fe)O synthesis, to Heidi H{\"o}fer for her support on the flank method calibration, to Detlef Krau{\ss}e for his technical support at the electron microprobe, to Nobuyoshi Mi-yajima for TEM investigations and to Florian Heidelbach for SEM analyses. The manuscript was significantly improved by the comments of Andrew Berry and an anonymous reviewer. ML received financial support from the European Commission under the Marie Curie Action for Early Stage Training of Researchers within the 6th Framework Programme (contract number MEST-CT-2005-019700). SDJ is supported in part by the US NSF (EAR-0748707) and by the David and Lucile Packard Foundation.",

year = "2011",

month = dec,

doi = "10.1007/s00410-011-0649-9",

language = "English (US)",

volume = "162",

pages = "1249--1257",

journal = "Contributions to Mineralogy and Petrology",

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T1 - Microanalysis of the iron oxidation state in (Mg,Fe)O and application to the study of microscale processes

AU - Longo, Micaela

AU - McCammon, Catherine A.

AU - Jacobsen, Steven D.

N1 - Funding Information: Acknowledgments We are grateful to Stephen Mackwell for supplying some of the samples examined in this study, to Hugh O’Neill for valuable advice concerning (Mg,Fe)O synthesis, to Heidi Höfer for her support on the flank method calibration, to Detlef Krauße for his technical support at the electron microprobe, to Nobuyoshi Mi-yajima for TEM investigations and to Florian Heidelbach for SEM analyses. The manuscript was significantly improved by the comments of Andrew Berry and an anonymous reviewer. ML received financial support from the European Commission under the Marie Curie Action for Early Stage Training of Researchers within the 6th Framework Programme (contract number MEST-CT-2005-019700). SDJ is supported in part by the US NSF (EAR-0748707) and by the David and Lucile Packard Foundation.

PY - 2011/12

Y1 - 2011/12

N2 - We report application of the flank method using the electron microprobe to a suite of twelve (Mg,Fe)O samples with composition 2-47 wt% Fe and Fe3+/ΣFe=1 to 11%, where Fe3+/ΣFe was determined independently using Mössbauer spectroscopy on the same grains used for the flank method measurements. A calibration curve of the form Fe2+=A+B× (ΣFe)2+C× (Lβ/Lα) was fit to the data and gave excellent agreement between Fe3+/ΣFe calculated from the flank method and Fe3+/ΣFe determined using Mössbauer spectroscopy. We found the method to be sufficiently sensitive to determine meaningful variations in Fe3+/ΣFe for geophysically relevant compositions of (Mg,Fe)O (<25 wt% Fe), and calibration parameters remained constant within experimental uncertainty over the course of the entire study (20 months). Flank method measurements on an inhomogeneous sample of synthetic (Mg,Fe)O showed evidence of diffusion processes resulting from rupture of the capsule during the high-pressure experiment and the possibility to measure Lβ/Lα variations with a spatial resolution of a few microns. We detected the presence of exsolved magnesioferrite in a suite of (Mg,Fe)O single crystals using transmission electron microscopy and Mössbauer spectroscopy. Flank method measurements on the same suite of single crystals showed enhanced Fe3+/ΣFe values, consistent with the presence of magnesioferrite even though the grains were too small to be resolved by conventional electron microprobe measurements.

AB - We report application of the flank method using the electron microprobe to a suite of twelve (Mg,Fe)O samples with composition 2-47 wt% Fe and Fe3+/ΣFe=1 to 11%, where Fe3+/ΣFe was determined independently using Mössbauer spectroscopy on the same grains used for the flank method measurements. A calibration curve of the form Fe2+=A+B× (ΣFe)2+C× (Lβ/Lα) was fit to the data and gave excellent agreement between Fe3+/ΣFe calculated from the flank method and Fe3+/ΣFe determined using Mössbauer spectroscopy. We found the method to be sufficiently sensitive to determine meaningful variations in Fe3+/ΣFe for geophysically relevant compositions of (Mg,Fe)O (<25 wt% Fe), and calibration parameters remained constant within experimental uncertainty over the course of the entire study (20 months). Flank method measurements on an inhomogeneous sample of synthetic (Mg,Fe)O showed evidence of diffusion processes resulting from rupture of the capsule during the high-pressure experiment and the possibility to measure Lβ/Lα variations with a spatial resolution of a few microns. We detected the presence of exsolved magnesioferrite in a suite of (Mg,Fe)O single crystals using transmission electron microscopy and Mössbauer spectroscopy. Flank method measurements on the same suite of single crystals showed enhanced Fe3+/ΣFe values, consistent with the presence of magnesioferrite even though the grains were too small to be resolved by conventional electron microprobe measurements.

KW - Electron microprobe

KW - Ferropericlase

KW - Flank method

KW - Iron oxidation state

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Microanalysis of the iron oxidation state in (Mg,Fe)O and application to the study of microscale processes

Abstract

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