Organic-Mediated Formation and Spectroscopic Characterization of Fe-Mg Carbonates: Laboratory Insights into Martian Carbonate Mineralogy

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 by the hydrothermal method in the laboratory. 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 to understand of 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 (CO_3^(2-)) 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. In addition, synthesis of siderite-magnesite solid solution was performed under hydrothermal conditions, where reduced organic compounds played a key role in mineral formation, which would provide experimental constraints on the geological and geochemical pathways of carbonate formation on Mars.