Martian Smectites Formation Regulated by Environmental CO₂ and Si

Despite the anticipated abundant carbonates due to historical atmospheric CO₂ levels, Mars presents a geological puzzle with MgFe-smectites dominating the Noachian and early Hesperian terrains, contrasted by sparse carbonate deposits. To address this point, we explored the impact of CO₂ on MgFe-smectite formation, emphasizing the role of variable Si concentrations within the simulated Martian environment. Hydrothermal experiments, conducted under a constant CO₂ concentration (C0.5) and varying Si concentrations (Si0.5 to Si4), reveal a transformation from pyroaurite to MgFe-smectite via lizardite as an intermediary phase. This transformation underscores the crucial role of Si in this mineral sequence. Notably, experiments demonstrate that the interlayer CO₃²⁻ in pyroaurite is released into aqueous environments during the mineral conversion, potentially impacting the Martian CO₂ budget. These findings could explain isolated carbonate outcrops and the possibility of hydrotalcite-group minerals on Mars today. Further Mars exploration should consider identifying hydrotalcite-group minerals for their implications on the planet's climate and habitability.