A Spectroscopic Study of Mars-Analog Materials with Amorphous Sulfate and Chloride Phases: Implications for Detecting Amorphous Materials on the Martian Surface

This repository contains the raw and baseline or continuum corrected data associated with the manuscript entitled: A Spectroscopic Study of Mars-Analog Materials with Amorphous Sulfate and Chloride Phases: Implications for Detecting Amorphous Materials on the Martian Surface This work is being submitted to The Planetary Science Journal ABSTRACT The Chemistry and Mineralogy X-ray diffraction (XRD) instrument aboard the Curiosity rover has consistently identified substantial amorphous material at Gale Crater. The amorphous component is compositionally variable, but often includes elevated sulfur and iron, suggesting that amorphous ferric sulfate (AFS) may be present. Understanding the spectral changes of common Martian materials exposed to ferric sulfate brines as they desiccate to AFS is a key step in bridging the gap between simple mixing studies and analyses of complex/realistic reaction assemblages. Visible and near-infrared reflectance (VNIR), mid-infrared attenuated total reflectance (MIR, FTIR-ATR), and Raman spectra, along with XRD data are presented for basaltic glass, hematite, gypsum, nontronite, and magnesite, each at three grain sizes (<25, 25-63, and 63-180 μm), mixed with ferric sulfate alone or also with NaCl, hydrated through deliquescence, and then rapidly desiccated in 11% relative humidity or via vacuum. All desiccated products are partially or completely XRD amorphous; crystalline phases include starting materials and trace precipitates, leaving the bulk of the ferric sulfate in the amorphous fraction. Due to considerable spectral masking, the detectability of AFS is highly dependent on spectroscopic technique and the observed mineral assemblage. This has strong implications for remote and in-situ observations of Martian samples which include an amorphous component. AFS is only identifiable in VNIR spectra for magnesite, nontronite, and gypsum samples; hematite and basaltic glass samples appear similar to pure materials. Sulfate features dominate Raman spectra for nontronite and basaltic glass samples; the analog material dominates Raman spectra of hematite and gypsum samples. MIR spectra reveal all end members most clearly except for basaltic glass samples, where the analog material is almost completely masked. NaCl leads to similar FTIR-ATR and Raman features, regardless of analog material. Associated photographs of samples in this project can be found at: https://www.lionsandlamms.com/ This research was supported by NSF award #1819209.