Abstract The identification of siderite-magnesite solid solutions provides important constraints on habitable environments on Mars. It offers insights into geochemical conditions, such as redox state and the availability of divalent cations, that could support carbonate formation. In this study, a series of pure siderite-magnesite solid solutions were synthesized via an organic-mediated hydrothermal method, a process in which organic compounds can influence carbonate nucleation and growth by complexing metal cations, templating mineral surfaces, modifying crystal growth kinetics, and stabilizing metastable phases under low-temperature and low-supersaturation conditions relevant to early Earth and Martian settings. ICP-OES was employed to determine the Fe2⁺ and Mg2⁺ contents, thereby confirming the compositions of the synthesized magnesite-siderite solid solutions. X-ray diffraction (XRD) was used to check the purity and homogeneity of synthesized magnesite-siderite solid solutions and help in understanding magnesite-siderite solid solutions in Gale Crater. The Raman spectra of synthesized samples were measured and compared with the Raman spectra measured by SHERLOC and SuperCam Raman at different sites to help the magnesite-siderite solid solutions identified in Jezero Crater. Linear relationships between main Raman peak positions (v1) of carbonate ion (CO32−) and mole percent of magnesium ions (Mg#) were established (R2=0.997), and were used to predict the Mg# of magnesite-siderite solid solutions within Jezero crater. The organic-mediated hydrothermal method used in this study suggests a newly recognized pathway for the formation of carbonates on Mars. Moreover, the pure-phase XRD and Raman datasets established in this study can provide solid spectral references for carbonate identification by current and future Mars missions.
Shi et al. (Tue,) studied this question.