Nanoscale\nAnalyses of X‑ray Amorphous Material\nfrom Terrestrial Ultramafic Soils Record Signatures of Environmental\nConditions Useful for Interpreting Past Martian Conditions

The secondary mineral assemblage of martian rocks and\nsediments\nis critical to the interpretation of past conditions on Mars. X-ray\namorphous material that is variably Mg/Fe/Si-rich and Al-poor, and\nthat likely contains secondary alteration products, makes up between\n15 and 73 wt % of Gale crater materials measured by the CheMin instrument\nand is also prevalent on the martian surface in other locations. Despite\nits prevalence, the structure and origin of this material and its\nimplications for past martian environments remains unknown. Here,\nwe employ transmission electron microscopy and synchrotron microprobe\nanalyses of Fe/Si/Mg-rich and Al-poor ultramafic soils from the mediterranean\nclimate Klamath Mountains of California and subarctic climate Tablelands\nof Newfoundland, Canada to help interpret environmental conditions\nduring the formation of chemically similar X-ray amorphous material\nin Gale crater, Mars. X-ray amorphous material includes globular amorphous\nsilica and chemically heterogeneous nanospherical amorphous material\nand nanocrystalline phases. Amorphous silica is present only in soils\nthat undergo extensive periods of cyclic freezing conditions. X-ray\namorphous material from the subarctic Tablelands is significantly\nricher in Mg and Si than material from the warmer Klamath Mountains.\nNanocrystallites in both examined soils are richer in Fe than the\ntruly amorphous material. However, Fe-rich nanocrystallites contain\nsignificantly more Mg and Si in the subarctic Tablelands, whereas\nKlamath Mountains soils contain highly Fe-enriched nanocrystallites\nincorporating little Mg and Si and potentially contain nanocrystalline\nsmectites. These characteristics provide helpful identifiers to interpret\npast environmental conditions during the formation of X-ray amorphous\nmaterial both in situ and in returned samples from Mars.