Integrated Micro to Nano-Scale Characterization of Hydrous Sulphate Mineral-Jarosite in Kachchh, Gujarat, India: Implication for Mars

The recent Martian exploration mission has provided substantial evidence for the presence of hydrous sulphate minerals, especially in the Gale Crater and Meridiani Planum. These findings are crucial for understanding the past climate, water activity, and geological history of early Mars. Studying the sulphate formation process, particularly jarosite, has become increasingly important. In this context, terrestrial analog sites with similar mineral deposits can serve as effective models for exploring and analyzing sulphate deposits in detail. The Matanomadh and Harudi formations of Kachchh, Gujarat, India, were chosen as Martian analog sites because they expose well-preserved, clay-rich jarosite layers that may help better understand paleo-environmental conditions during Martian alteration. Here, jarosite is found alongside grey carbonaceous shale, weathered basalt, and gypsum, typically appearing as lenses of variable width, interconnected veins, or veinlets. Pure jarosite samples were collected after detailed field studies from the Matanomadh and Harudi formations of Kachchh. Powdered samples were characterized using X-Ray Diffraction (XRD), High-Resolution Transmission Electron Microscopy (HR-TEM), Field Emission Scanning Electron Microscopy (FE-SEM), X-Ray Photoelectron Spectroscopy (XPS), and Elemental Analyzer-Isotope Ratio Mass Spectrometry (EA-IRMS) for sulfur isotope analysis. All XRD patterns were analyzed with the FullProf program using Rietveld refinement, employing the R-3m space group. The average a- and c-cell dimensions for jarosite were calculated as a = 7.3028 Å and c = 16.6376 Å. The XRD diffractogram displays a distinct peak at (006) at 2θ = 32.29°. FE-SEM images show that jarosite crystals have well-formed pseudohexagonal shapes with defined faces and edges. HR-TEM analysis indicates the dominance of sodium (Na), and elemental mapping confirms homogeneous grains. XPS analysis of jarosite revealed prominent peaks for Fe2p_3/2 and S2p at approximately 713.4 eV and 169.9 eV, respectively. S2p peaks were also observed in the host shale rock. δ³⁴S values for jarosite (-8.4 to -16‰) are close to values typical of supergene or steam-heated hydrous sulphates derived from pyrite or H₂S oxidation. The cell dimensions obtained from XRD data agree with literature values, confirming the mineral as Natrojarosite. The peak position of the (006) reflection in natrojarosite differs from that of jarosite. In this sample group, iron (Fe) exists in the +3 oxidation state, as confirmed by XPS. Based on the presence of sulfur (S -1) peaks in the associated shale, it is inferred that shale may serve as a sulfur source for natrojarosite formation in the current study area under acidic, oxidizing conditions.