WARM AND WET CONDITIONS PROMOTE NANOCRYSTALLINITY IN FE-RICH X-RAY AMORPHOUS MATERIAL WHILE COOL AND WET CONDITIONS PROMOTE FORMATION OF PURELY AMORPHOUS SI/FE-RICH MATERIAL IN TERRESTRIAL ULTRAMAFIC SOILS CHEMICALLY RELEVANT TO MARS

Analyses of X-ray diffraction data from the CheMin instrument with FULLPAT have documented X-ray amorphous material in all rocks and soils analyzed at Gale Crater, Mars to date. This material is both Fe-rich and Despite the prevalence of this material on Mars, its identity, characteristics, and formation mechanisms remain unknown. To investigate Fe-rich X-ray amorphous material in terrestrial settings, we analyzed ultramafic soils from the mediterranean climate Klamath Mountains of northern California and the subarctic climate Tablelands of Newfoundland Canada using HRTEM and synchrotron techniques.TEM indicates the presence of three X-ray amorphous material morphologies. The first consists of amorphous silica globules up to ~200 nm across. The second is chemically amorphous Fe/Mg-rich silicates possessing an allophanic nanospherical texture but ≤15.76 wt%. Al₂O₃ in the Klamaths and 0 wt.% Al₂O₃ in the Tablelands. The third is composed of nanocrystalline domains, primarily Fe-oxides, sometimes intimately intermixed with the nanospherules. The amorphous silica globules and the amorphous Mg/Fe-silicate nanospherules are present in both locations, though globular material is more prevalent in the subarctic Tablelands soils, forming clusters up to several µm across. Fe-rich nanocrystalline domains are primarily found in Klamath soils and when observed in Tablelands soils are interspersed within a primarily amorphous matrix. We find Fe-rich X-ray amorphous material present in all examined soils, but warm and wet conditions appear to promote nanocrystallinity while cool and wet conditions promote formation of purely amorphous Si/Fe-rich material, observations that may help interpret future samples from Mars.