Martian Smectites Formation Regulated by Environmental CO ₂ and Si

Abstract Despite the anticipated abundant carbonates due to historical atmospheric CO 2 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 CO 2 on MgFe‐smectite formation, emphasizing the role of variable Si concentrations within the simulated Martian environment. Hydrothermal experiments, conducted under a constant CO 2 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 CO 3 2− in pyroaurite is released into aqueous environments during the mineral conversion, potentially impacting the Martian CO 2 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.