A decade of quantitative mineralogy on Mars: results from the CheMin X-ray diffractometer on the Mars Science Laboratory rover Curiosity

For more than a decade, the CheMin X-ray diffraction instrument on the Mars Science Laboratory rover Curiosity has been returning definitive and quantitative mineralogical and mineral-chemistry data from ~3.5-billion-year-old (Ga) sediments in Gale crater, Mars.To date, 36 drilled rock samples and 3 scooped soil samples have been analyzed over the course of a 29+ km transit.These samples document the mineralogy of more than 600 vertical meters of flat-lying fluvial, lacustrine and aeolian sediments that comprise the lower strata of the central mound of Gale crater (Aeolis Mons; informally known as Mt.Sharp) and the surrounding plains (Aeolis Palus).The principal mineralogy of the sediments is basaltic, with evidence of early and late-stage diagenetic overprinting.The rocks in many cases preserve much of their primary mineralogy and sedimentary features, suggesting that they were never strongly heated or deformed.Using aeolian soil composition as a proxy for the composition of the deposited and lithified sediment, it appears that in many cases diagenetic changes observed are principally isochemical.Exceptions to this trend include secondary nodules, calcium sulfate veining, and rare Si-rich alteration halos.A striking hematite-rich feature in lower Mt.Sharp called Vera Rubin ridge is interpreted to be lake sediment diagenetically altered by dense, silica-poor brines.A surprising and yet poorly understood observation is that nearly all of the ~3.5 Ga old sedimentary rocks analyzed to date contain 15-70 wt.% X-ray amorphous material.Overall, this 600+ meter vertical section of sedimentary rock explored on lower Mt.Sharp documents a perennial shallow lake environment grading upward into alternating lacustrine/fluvial and aeolian environments.Highlights of CheMin's results from Mars include: The first quantitative mineralogical analysis of the global Mars soil [1-2]; Discovery and characterization of the first habitable environment on another planet [3-5]; Evidence of low Hesperian PCO2, calling into question the role of CO2-based greenhouse warming [6]; Evidence for a highly diverse basalt mineralogy on early Mars [7]; and Changes in clay mineral and Fe-oxide chemistry, documenting the drying out and oxidation of the Martian hydrosphere [8].All data and open access publications can be downloaded from the CheMin ODR website: http://odr.io/chemin.Figure 1.Changes in Fe-oxides, clay mineralogy and sulfate abundance along Curiosity's track from Yellowknife Bay to the Clay-Sulfate transition.