Anaerobic Microscopic Analysis of Ferrous Saponite and Its Sensitivity to Oxidation by Earth’s Air: Lessons Learned for Analysis of Returned Samples from Mars and Carbonaceous Asteroids

Ferrous saponite is a secondary mineral that can be used to reveal the redox state of past aqueous environments on Mars. In mineralogical analyses for ferrous saponite formed in laboratory simulations or contained in future returned samples from Mars, its oxidation by the Earth’s air could be proble...

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Autores principales:	Natsumi Noda, Shohei Yamashita, Yoshio Takahashi, Megumi Matsumoto, Yuma Enokido, Kana Amano, Takahiro Kawai, Hiroshi Sakuma, Keisuke Fukushi, Yasuhito Sekine, Tomoki Nakamura
Formato:	article
Lenguaje:	EN
Publicado:	MDPI AG 2021
Materias:	Fe-bearing clay minerals ferrous saponite redox chemistry micro XRD STXM XANES Mineralogy QE351-399.2
Acceso en línea:	https://doaj.org/article/6b4c33dbf2c7472cb4f2c04fae993a61
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spelling	oai:doaj.org-article:6b4c33dbf2c7472cb4f2c04fae993a612021-11-25T18:26:33ZAnaerobic Microscopic Analysis of Ferrous Saponite and Its Sensitivity to Oxidation by Earth’s Air: Lessons Learned for Analysis of Returned Samples from Mars and Carbonaceous Asteroids10.3390/min111112442075-163Xhttps://doaj.org/article/6b4c33dbf2c7472cb4f2c04fae993a612021-11-01T00:00:00Zhttps://www.mdpi.com/2075-163X/11/11/1244https://doaj.org/toc/2075-163XFerrous saponite is a secondary mineral that can be used to reveal the redox state of past aqueous environments on Mars. In mineralogical analyses for ferrous saponite formed in laboratory simulations or contained in future returned samples from Mars, its oxidation by the Earth’s air could be problematic due to the high redox sensitivity. Here, we performed micro X-ray diffraction and scanning transmission X-ray microscopy analyses for a single particle of synthesized ferrous saponite without any exposure to air. The sample was reanalyzed after air exposure for 10–18 h to assess the adequacy of our anoxic preparation/measurement methods and the impacts of air on the sample. We found that the crystal structures agreed with ferrous saponite, both before and after air exposure; however, ferrous iron in saponite was partially oxidized, at least until 0.1–1 μm from the surface, after air exposure at the submicron scale, forming micro-vein-like Fe(III)-rich features. Together with our results of infrared spectroscopy of ferrous saponite, we showed that oxidation of octahedral iron occurred rapidly and heterogeneously, even in a short time of air exposure without any structural rearrangement. Since ferrous saponite is expected to exist on carbonaceous asteroids and icy dwarf planets, our methodology is also applicable to mineralogical studies of samples returned from these bodies.Natsumi NodaShohei YamashitaYoshio TakahashiMegumi MatsumotoYuma EnokidoKana AmanoTakahiro KawaiHiroshi SakumaKeisuke FukushiYasuhito SekineTomoki NakamuraMDPI AGarticleFe-bearing clay mineralsferrous saponiteredox chemistrymicro XRDSTXMXANESMineralogyQE351-399.2ENMinerals, Vol 11, Iss 1244, p 1244 (2021)
institution	DOAJ
collection	DOAJ
language	EN
topic	Fe-bearing clay minerals ferrous saponite redox chemistry micro XRD STXM XANES Mineralogy QE351-399.2
spellingShingle	Fe-bearing clay minerals ferrous saponite redox chemistry micro XRD STXM XANES Mineralogy QE351-399.2 Natsumi Noda Shohei Yamashita Yoshio Takahashi Megumi Matsumoto Yuma Enokido Kana Amano Takahiro Kawai Hiroshi Sakuma Keisuke Fukushi Yasuhito Sekine Tomoki Nakamura Anaerobic Microscopic Analysis of Ferrous Saponite and Its Sensitivity to Oxidation by Earth’s Air: Lessons Learned for Analysis of Returned Samples from Mars and Carbonaceous Asteroids
description	Ferrous saponite is a secondary mineral that can be used to reveal the redox state of past aqueous environments on Mars. In mineralogical analyses for ferrous saponite formed in laboratory simulations or contained in future returned samples from Mars, its oxidation by the Earth’s air could be problematic due to the high redox sensitivity. Here, we performed micro X-ray diffraction and scanning transmission X-ray microscopy analyses for a single particle of synthesized ferrous saponite without any exposure to air. The sample was reanalyzed after air exposure for 10–18 h to assess the adequacy of our anoxic preparation/measurement methods and the impacts of air on the sample. We found that the crystal structures agreed with ferrous saponite, both before and after air exposure; however, ferrous iron in saponite was partially oxidized, at least until 0.1–1 μm from the surface, after air exposure at the submicron scale, forming micro-vein-like Fe(III)-rich features. Together with our results of infrared spectroscopy of ferrous saponite, we showed that oxidation of octahedral iron occurred rapidly and heterogeneously, even in a short time of air exposure without any structural rearrangement. Since ferrous saponite is expected to exist on carbonaceous asteroids and icy dwarf planets, our methodology is also applicable to mineralogical studies of samples returned from these bodies.
format	article
author	Natsumi Noda Shohei Yamashita Yoshio Takahashi Megumi Matsumoto Yuma Enokido Kana Amano Takahiro Kawai Hiroshi Sakuma Keisuke Fukushi Yasuhito Sekine Tomoki Nakamura
author_facet	Natsumi Noda Shohei Yamashita Yoshio Takahashi Megumi Matsumoto Yuma Enokido Kana Amano Takahiro Kawai Hiroshi Sakuma Keisuke Fukushi Yasuhito Sekine Tomoki Nakamura
author_sort	Natsumi Noda
title	Anaerobic Microscopic Analysis of Ferrous Saponite and Its Sensitivity to Oxidation by Earth’s Air: Lessons Learned for Analysis of Returned Samples from Mars and Carbonaceous Asteroids
title_short	Anaerobic Microscopic Analysis of Ferrous Saponite and Its Sensitivity to Oxidation by Earth’s Air: Lessons Learned for Analysis of Returned Samples from Mars and Carbonaceous Asteroids
title_full	Anaerobic Microscopic Analysis of Ferrous Saponite and Its Sensitivity to Oxidation by Earth’s Air: Lessons Learned for Analysis of Returned Samples from Mars and Carbonaceous Asteroids
title_fullStr	Anaerobic Microscopic Analysis of Ferrous Saponite and Its Sensitivity to Oxidation by Earth’s Air: Lessons Learned for Analysis of Returned Samples from Mars and Carbonaceous Asteroids
title_full_unstemmed	Anaerobic Microscopic Analysis of Ferrous Saponite and Its Sensitivity to Oxidation by Earth’s Air: Lessons Learned for Analysis of Returned Samples from Mars and Carbonaceous Asteroids
title_sort	anaerobic microscopic analysis of ferrous saponite and its sensitivity to oxidation by earth’s air: lessons learned for analysis of returned samples from mars and carbonaceous asteroids
publisher	MDPI AG
publishDate	2021
url	https://doaj.org/article/6b4c33dbf2c7472cb4f2c04fae993a61
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Anaerobic Microscopic Analysis of Ferrous Saponite and Its Sensitivity to Oxidation by Earth’s Air: Lessons Learned for Analysis of Returned Samples from Mars and Carbonaceous Asteroids

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