Abstract
The Chemistry and Mineralogy (CheMin) X-ray diffraction (XRD) instrument onboard the Mars Science Laboratory (MSL) Curiosity rover has provided unprecedented in-situ mineralogical data from the lacustrine mudstones of Gale Crater, Mars. Reconstructing the ancient depositional and diagenetic history of these mudstones requires high-precision crystallographic analysis. In this study, we present a systematic re-evaluation and in-situ mineralogical mapping of the Sheepbed member (Yellowknife Bay) and the Murray formation (Mount Sharp) mudstone samples using advanced Rietveld refinement protocols. By implementing sophisticated models for turbostratic disorder in clay minerals and utilizing the Partial Or No Known Crystal Structure (PONKCS) method for amorphous phase quantification, we refined the mineral abundances, unit-cell parameters of major crystalline phases, and the composition of the amorphous components. Our results reveal a pronounced mineralogical gradient: lower lacustrine units are dominated by trioctahedral smectites (saponite) and primary igneous minerals, indicating a circumneutral, low-salinity aqueous environment. Conversely, the overlying Murray formation shows a progressive enrichment in dioctahedral smectites, hematite, jarosite, and amorphous silica, pointing to an increasingly acidic, saline, and highly oxidizing depositional or early diagenetic regime. This high-resolution mineralogical mapping provides critical constraints on the thermodynamic and kinetic conditions of ancient Martian aqueous systems, reinforcing the temporal evolution of habitability within Gale Crater.
