The Crystal Chemistry of Fe3+ in Nontronite: Implications for Paleoenvironmental Evolution on Mars

We synthesized a series of samples with varying Si/Al/Fe molar ratios under controlled hydrothermal conditions. The resulting solid products were characterized using powder X-ray diffraction, infrared spectroscopy, electron microscopy, and Mössbauer spectroscopy, to elucidate structural characteristics of nontronite. X-ray diffraction (XRD) data shows changed crystallinity of these synthesized samples. Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM) data illustrated the different morphology and microstructure of samples. Mid infrared spectroscopy (MIR) and Visible-shortwave infrared reflectance (VSWIR) showed change of characteristic vibrations of samples, including band shift and band depth. Mössbauer spectra data identified and quantified the coordination of Fe3+ cations in these samples, including tetrahedral Fe3+ and octahedral Fe3+.