Chemical and spectroscopic investigations of K‐H 3 O‐Na jarosite solid solutions applicable for Mars explorations

Jarosite is the first definitely discovered ferric sulfate mineral on Mars, indicating a highly acidic environment in Martian history. K‐H 3 O and Na‐H 3 O jarosite solid solutions were synthesized under hydrothermal conditions. Phase identifications and chemical compositions were determined by X‐ray diffraction and scanning electron microscopy coupled with energy dispersive spectroscopy. Raman spectra of those two series of jarosite solid solutions show systematic spectral changes with varying alkali content. When chemical ratios of K/(K + H 3 O), in K‐H 3 O jarosite solid solutions, increase from 0% to 88%, their Raman peaks exhibit systematic shifts: ν 2 (SO 4 ) 2− (from 424.7 to 434.3 cm −1 ), ν 4 (SO 4 ) 2‐ (from 619.6 to 623.8 cm −1 ), ν 1 (SO 4 ) 2‐ (from 1,011.8 to 1,006.1 cm −1 ) and, ν 3 (SO 4 ) 2− (from 1,165.4 to 1,152.9 cm −1 ). Near‐infrared and mid‐infrared spectra were also collected for the spectral library of Mars remote‐sensing studies. The detailed chemical and spectroscopic studies of K‐H 3 O‐Na jarosite solid solutions would contribute to their potential discoveries on Mars by future Mars missions (e.g., Mars 2020 and ExoMars). Copyright © 2017 John Wiley & Sons, Ltd.