The range of redox states was Fe 3+/ΣFe = 0 to 0.06 ± 0.01 as determined by both XAS and, for short integration times, Mössbauer. Samples were characterized by inductively coupled plasma optical emission spectrometry, powder X-ray diffraction, Fe K-edge X-ray absorption spectroscopy (XAS), Mössbauer spectroscopy, and visible/near-infrared (VNIR) reflectance spectroscopy. In this study, eight Fe 2+-bearing smectites were synthesized from Fe 2+-Mg-Al silicate gels at 200☌ under anoxic conditions. In general, the physicochemical properties of ferrous smectites are poorly studied because they are susceptible to air oxidation. Ferrous trioctahedral smectites are thermodynamically predicted products of basalt weathering on early Mars, but to date only Fe 3+-bearing dioctahedral smectites have been identified from orbital observations. Widespread detections of phyllosilicates in Noachian terrains on Mars imply a history of near-surface fluid-rock interaction.
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