¹Anuja Sreejayan et al. (>10)
Journal of Geophysical Reseacrh: Planets (in Press) Link to Article [https://doi.org/10.1029/2025JE009544]
¹Department of Geology, University of Kerala, Thiruvananthapuram, Kerala, India
Published by arrangement with John Wiley & Sons

This study reports the first occurrence of melanterite (Fe2+SO4·7H2O), a secondary hydrous sulfate mineral, in Peninsular India and examines its formation through the oxidative weathering of marcasite associated with lignite in Neyveli, Tamil Nadu. The marcasite was exposed to normal atmospheric conditions, and melanterite was formed within 23 days via oxidative weathering. Melanterite occurs as a yellow, prismatic to fibrous, translucent crystal, either as individual fibers or clusters. Though melanterite is mineralogically characterized through different techniques like X-ray diffraction, scanning electron microscopy-energy dispersive X-ray spectroscopy, and electron probe microanalysis (EPMA), the results obtained from EPMA [(Fe0.839 Cu0.000355 Zn0.000466 Ni0.000545) SO4·7H2O] closely match the composition of standard melanterite. Fourier Transform Infrared spectroscopy identified key vibrational peaks for sulfates (450–480 cm−1) and water molecules (1,544–1,650 cm−1), while laser Raman spectroscopy provided evidence for the characteristic vibration of melanterite at 976 cm−1. Hyperspectral analysis also discerned the characteristic Fe2+ peak (0.45–0.9 μm) of melanterite. A spectrum, comparable to that of melanterite, obtained through Compact Reconnaissance Imaging Spectrometer for Mars data from the Ceti Mensa region on Mars, where it is associated with a polysulfate deposit. Since melanterite forms under acidic and oxidizing conditions in low moisture, its occurrence can provide insights into the environmental conditions under which sulfate forms. Thus, this study can provide insights into studying transient wet conditions on Mars.

^1,2Devan M. Nisson et al. (>10)
Journal of Geophysical Research: Planets (in Press) Open Access Link to Article [https://doi.org/10.1029/2025JE009395]
¹Department of Geosciences, Princeton University, Princeton, NJ, USA
²NASA Postdoctoral Program Fellow, NASA Ames Research Center, Moffett Field, CA, USA
Published by arrangement with John Wiley & Sons

Serpentinization produces hydrogen and methane through abiotic water-rock interactions, potentially supporting chemotrophic life in planetary subsurface environments. Serpentine deposits in the Martian Noachian landscapes of Nili Fossae and the Southern Highlands have been considered as potential paleo-habitable zones. However, the geochemical and physical conditions of Martian serpentinization fluids are poorly constrained because of limited data on serpentinite composition and formation environment. Furthermore, the co-occurrence of magnesite and magnesium-enriched serpentines on Mars remains enigmatic. To address such gaps, we investigated antigorite-magnesite paleo-serpentine bodies along the Highland-Vijayan suture of Sri Lanka as Martian analog sites, using thermodynamic batch reaction models to constrain alteration fluids and the production of primary (H2) and secondary (CH4) serpentinization products. Geochemist’s Workbench models combined field X-Ray Fluorescence (XRF) observations with varied protolith compositions (ultramafic or gneissic), precursor fluids (seawater or freshwater), temperatures (100–600°C), volumetric water-to-rock ratios (1–100,000), and CO2 partial pressures (0.01–1 bar). Models successfully reproduced the co-occurrence of antigorite and magnesite observed on Mars, with both minerals forming at 100°C across water-to-rock ratios. Despite their Mg-enriched composition, ultramafic protoliths produced H2 yields (up to 229 mmol/kg at W/R 1 at 100°C), supporting chemotrophic populations up to 107.5 cells/mL. Geochemical models indicate Mg enrichment from ultramafic mineralogy and Fe contribution from regional gneisses. Our thermodynamic equilibrium results show that Mg-rich serpentine systems with sufficient ferrous iron can produce biologically significant H2, establishing Sri Lankan serpentinites as valuable analogs for Noachian Mars habitability.