¹M. M. Morris, ¹J. A. Hurowitz, ¹L. Ehm
Journal of Geophysical Research: Planets, 131, e2026JE010007
Link to Article [DOI: 10.1029/2026JE010007]
¹Department of Geosciences, Stony Brook University, Stony Brook, NY, USA

Published by arrangement with John Wiley & Sons

Fe-Mg carbonates on Mars preserve key evidence of past aqueous chemistry and climate, yet their formation conditions remain poorly constrained. We conducted low-temperature (∼25°C) anoxic precipitation experiments under Mars-like conditions, systematically varying pH, Fe:Mg ratio, Ca²⁺ content, and carbonate saturation state. Results show initial pH and saturation state as primary controls: near-neutral pH favored siderite (FeCO₃) and chukanovite (Fe₂(CO₃)(OH)₂) precipitation, while alkaline conditions promoted the precipitation of hydrated Mg-carbonate and Fe-substituted Mg-hydroxide and layered double hydroxides. Ca²⁺ suppressed amorphous Fe-carbonate precursor precipitation, enhancing the growth of rhombohedral carbonate and enabling partial Ca²⁺ substitution. A limited number of elevated temperature experiments (50°C) did not enhance Mg²⁺ substitution in siderite, but instead resulted in the precipitation of very high-magnesium calcite (MgCa(CO₃)₂) overgrowths. Mg²⁺ incorporation into siderite (at the level of ∼10 mol%) occurred only under low Fe:Mg ratios and high magnesite (MgCO₃) saturation, highlighting kinetic barriers to Mg²⁺ substitution.