Alison Beehr
Department of Earth and Planetary Sciences
Washington University in St. Louis
Advisor: Jeffrey G. Catalano

Abstract
Data collected by the OMEGA spectrometer and the CRISM instrument indicate the presence of iron-bearing phyllosilicates on Mars' surface. Identified species include nontronite, kaolinite, and montmorillonite; notable is the occurrence of ferric smectites. These units were deposited during the Noachian, which is thought to have had moist, reducing, and alkaline conditions. Such conditions favor the initial formation of ferrous iron-bearing phyllosilicates. Subsequent surface alteration events could then have oxidized these units. An understanding of the formation and oxidation of ferrous phyllosilicates can offer insight into the early Martian environment; this research explores a potential formation pathway of these phyllosilicates. To date, the work has focused on synthesizing a ferrous phyllosilicate through a hydrothermal sol-gel procedure and subsequently oxidizing it with H2O2, in order to characterize chemical and structural changes that occur upon oxidation of a ferrous phyllosilicate. The product was characterized in its inital and oxidized states by X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray absorption spectroscopy (XAS). H2O2 was used as it is likely the dominant oxidant currently present on Mars. Analyses indicate the initial product is a nanocrystalline 2:1 phyllosilicate containing Fe(II) in the octahedral sheet. Complete oxidation of this ferrous phyllosilicate by H2O2 disrupts the structure, driving some iron out of the octahedral sheet; but if the product is allowed to undergo further hydrothermal aging, it re-equilibrates. The oxidized product thus obtained contains Fe(III) distributed between the octahedral and tetrahedral sheet; this is common in nontronites. This indicates that oxidation of a ferrous phyllosilicate by H2O2 is a viable formation phase for Martian nontronite.Data collected by the OMEGA spectrometer and the CRISM instrument indicate the presence of iron-bearing phyllosilicates on Mars' surface. Identified species include nontronite, kaolinite, and montmorillonite; notable is the occurrence of ferric smectites. These units were deposited during the Noachian, which is thought to have had moist, reducing, and alkaline conditions. Such conditions favor the initial formation of ferrous iron-bearing phyllosilicates. Subsequent surface alteration events could then have oxidized these units. An understanding of the formation and oxidation of ferrous phyllosilicates can offer insight into the early Martian environment; this research explores a potential formation pathway of these phyllosilicates. To date, the work has focused on synthesizing a ferrous phyllosilicate through a hydrothermal sol-gel procedure and subsequently oxidizing it with H2O2, in order to characterize chemical and structural changes that occur upon oxidation of a ferrous phyllosilicate. The product was characterized in its inital and oxidized states by X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray absorption spectroscopy (XAS). H2O2 was used as it is likely the dominant oxidant currently present on Mars. Analyses indicate the initial product is a nanocrystalline 2:1 phyllosilicate containing Fe(II) in the octahedral sheet. Complete oxidation of this ferrous phyllosilicate by H2O2 disrupts the structure, driving some iron out of the octahedral sheet; but if the product is allowed to undergo further hydrothermal aging, it re-equilibrates. The oxidized product thus obtained contains Fe(III) distributed between the octahedral and tetrahedral sheet; this is common in nontronites. This indicates that oxidation of a ferrous phyllosilicate by H2O2 is a viable formation phase for Martian nontronite.