A Comparative Study of Gypsum Formation in the Atacama Desert (Chile) and Tiruchirappalli Badlands (India): Implications for Martian Paleoenvironments

Abstract Gypsum is a key mineral to reconstruct aqueous processes on Mars. Thus, this study compares gypsum from two contrasting terrestrial environments: the hyperarid Atacama Desert of Chile and the semi‐arid Tiruchirappalli Badlands of India, and its comparison with multiple sites on Mars, serving as end‐member analogs for Martian gypsum. Using field observations, petrography, X‐ray diffraction, scanning electron microscopy, energy‐dispersive spectroscopy, Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), and hyperspectral reflectance, we characterized samples from both localities. In Atacama, gypsum occurs as fibrous veinlets within mudstone, with coexisting bassanite and anhydrite. Whereas in Tiruchirappalli, it forms fracture‐filling veins with fluid inclusions and iron staining, and is associated with kaolinite‐hematite within the Cretaceous mudstones of the Karai Formation. Raman and FTIR confirm the presence of gypsum at both sites, with an additional anhydrite phase in Atacama. These sites exhibit similar hyperspectral absorption features that match those observed by CRISM at Olympia Undae, Columbus Crater, and Mawrth Vallis. When Atacama gypsum formed as a primary evaporite through groundwater evaporation under extreme aridity, Tiruchirappalli gypsum formed diagenetically, precipitating from sulfate‐rich fluids into fractures during burial and uplift, with tropical weathering. This spectral equivalence from different pathways shows that orbital spectra alone cannot determine gypsum genesis on Mars without geological context. The framework matches Atacama gypsum to Olympia Undae, Tiruchirappalli to Columbus Crater, and both to Mawrth Vallis. Fluid inclusions and endolithic communities highlight gypsum's potential to preserve biosignatures. Together, these findings strengthen interpretations of the Martian paleoenvironment and guide gypsum‐focused habitability assessments.