Superhydrous hematite and goethite: A potential water reservoir in the red dust of Mars?

Si Athena Chen; Peter J. Heaney; Jeffrey E. Post; Timothy B. Fischer; Peter J. Eng; Joanne E. Stubbs

doi:10.1130/G48929.1

Superhydrous hematite and goethite: A potential water reservoir in the red dust of Mars?

Si Athena Chen, Peter J. Heaney, Jeffrey E. Post, Timothy B. Fischer, Peter J. Eng, Joanne E. Stubbs

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

12 Scopus citations

Abstract

Water can be stored in nominally anhydrous minerals as substitutional hydroxyl, generating vast but commonly unrecognized H₂O reservoirs in ostensibly dry regimes. Researchers have long known that hematite (α-Fe₂O₃) can accommodate small concentrations of hydroxyl through the substitution of Fe³⁺ by 3H⁺. Our study of natural hematite has demonstrated the occurrence of “hydrohematite” phases that are 10–20 mol% deficient in Fe and accordingly contain 3.6–7.8 mol% structural water. Intergrown with natural hydrohematite samples were superhydrous goethite-like phases exhibiting an Fe deficiency of 10–20 mol% relative to endmember goethite (α-FeOOH). We synthesized hydrohematite in alkaline solutions (pH 9–12) at low temperatures (T < 200 °C) using fresh ferrihydrite as the transient precursor, and we observed a nonclassical crystallization pathway involving vacancy inoculation by Fe as nanocrystals evolved. The high level of incorporation of H2O in iron (hydr)oxides dramatically alters their behaviors as catalysts and pigments, and the presence of hydrohematite in rocks may rule out high-T diagenesis. We propose that hydrohematite is common in low-T occurrences of Fe oxide on Earth, and by extension it may inventory large quantities of water in apparently arid planetary environments, such as the surface of Mars.

Original language	English
Pages (from-to)	1343-1347
Number of pages	5
Journal	Geology
Volume	49
Issue number	11
DOIs	https://doi.org/10.1130/G48929.1
State	Published - Nov 2021
Externally published	Yes

Funding

We thank Katherine Crispin of the Penn State Materials Characterization Laboratory (The Pennsylvania State University, USA) for her generous help and suggestions with EPMA data collection. In addition, Trevor Clark, Haiying Wang, and Ke Wang assisted with FIB sample preparation and transmission electron microscopy data collection. We thank Florence T. Ling for collecting FTIR data for Hm at the Smith-sonian Institution (Washington, D.C., USA), and Xin Gu for discussions of geochemistry. We are grateful to Andreas Massanek of the Technische Universität Bergakademie (Freiberg, Germany) for sharing a sample of the “type” hydrohematite collected by J.F.A. Breithaupt in 1843. This work was funded by a seed grant from the Pennsylvania State University Biogeochemistry dual-title Ph.D. program and by U.S. National Science Foundation (NSF) grants EAR-1552211 and EAR-1925903. Synchrotron XRD was measured at GeoSoilEnviroCARS (The University of Chicago, Sector 13), Advanced Photon Source (APS), Argonne National Laboratory (ANL). GeoSoilEnviroCARS is supported by the NSF–Earth Sciences (grant EAR–1634415) and U.S. Department of Energy (DOE)–GeoSciences (grant DE-FG02-94ER14466). The APS is a DOE Office of Science User Facility operated by ANL under Contract No. DE-AC02-06CH11357. We thank Katherine Crispin of the Penn State Materials Characterization Laboratory (The Pennsylvania State University, USA) for her generous help and suggestions with EPMA data collection. In addition, Trevor Clark, Haiying Wang, and Ke Wang assisted with FIB sample preparation and transmission electron microscopy data collection. We thank Florence T. Ling for collecting FTIR data for Hm at the Smithsonian Institution (Washington, D.C., USA), and Xin Gu for discussions of geochemistry. We are grateful to Andreas Massanek of the Technische Universit?t Bergakademie (Freiberg, Germany) for sharing a sample of the ?type? hydrohematite collected by J.F.A. Breithaupt in 1843. This work was funded by a seed grant from the Pennsylvania State University Biogeochemistry dual-title Ph.D. program and by U.S. National Science Foundation (NSF) grants EAR-1552211 and EAR-1925903. Synchrotron XRD was measured at GeoSoilEnviroCARS (The University of Chicago, Sector 13), Advanced Photon Source (APS), Argonne National Laboratory (ANL). GeoSoilEnviroCARS is supported by the NSF?Earth Sciences (grant EAR?1634415) and U.S. Department of Energy (DOE)?GeoSciences (grant DE-FG02-94ER14466). The APS is a DOE Office of Science User Facility operated by ANL under Contract No. DE-AC02-06CH11357.

Funders	Funder number
Earth Sciences	EAR–1634415
NSF?Earth Sciences	1634415
Pennsylvania State University Biogeochemistry
Technische Universit?t Bergakademie
National Science Foundation	EAR-1925903, EAR-1552211
Smithsonian Institution
U.S. Department of Energy	DE-FG02-94ER14466
Office of Science
Argonne National Laboratory	DE-AC02-06CH11357
University of Chicago
Pennsylvania State University

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title = "Superhydrous hematite and goethite: A potential water reservoir in the red dust of Mars?",

abstract = "Water can be stored in nominally anhydrous minerals as substitutional hydroxyl, generating vast but commonly unrecognized H2O reservoirs in ostensibly dry regimes. Researchers have long known that hematite (α-Fe2O3) can accommodate small concentrations of hydroxyl through the substitution of Fe3+ by 3H+. Our study of natural hematite has demonstrated the occurrence of “hydrohematite” phases that are 10–20 mol% deficient in Fe and accordingly contain 3.6–7.8 mol% structural water. Intergrown with natural hydrohematite samples were superhydrous goethite-like phases exhibiting an Fe deficiency of 10–20 mol% relative to endmember goethite (α-FeOOH). We synthesized hydrohematite in alkaline solutions (pH 9–12) at low temperatures (T < 200 °C) using fresh ferrihydrite as the transient precursor, and we observed a nonclassical crystallization pathway involving vacancy inoculation by Fe as nanocrystals evolved. The high level of incorporation of H2O in iron (hydr)oxides dramatically alters their behaviors as catalysts and pigments, and the presence of hydrohematite in rocks may rule out high-T diagenesis. We propose that hydrohematite is common in low-T occurrences of Fe oxide on Earth, and by extension it may inventory large quantities of water in apparently arid planetary environments, such as the surface of Mars.",

author = "Chen, {Si Athena} and Heaney, {Peter J.} and Post, {Jeffrey E.} and Fischer, {Timothy B.} and Eng, {Peter J.} and Stubbs, {Joanne E.}",

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AU - Eng, Peter J.

AU - Stubbs, Joanne E.

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Superhydrous hematite and goethite: A potential water reservoir in the red dust of Mars?

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