Compositional imaging and spot analyses with the microprobe revealed distinct alteration textures and phases, suggesting weathering pathways involving the oxidation of iron in olivine and primary Fe 2+ oxides to form Fe 3+ oxides as well as the formation of aluminum phyllosilicates and magnesium phyllosilicates from feldspars and olivines, respectively, while pyroxene remained relatively unaltered. Primary mineralogy for all samples, as determined by point analyses with the microprobe and XRD, consisted of olivine, plagioclase, nepheline, augite, and titanomagnetite. Samples with strong 1.9 µm H 2O-related absorptions in VSWIR commonly exhibited absorption bands at 1.4, 2.2, and/or 2.3 µm, indicating the presence of clay minerals or silica as well as features at 0.5–0.9 mm indicative of ferric iron oxides. As an analog for the weathering of alkaline basaltic rocks on Mars, a suite of rocks visually identified to have different degrees of alteration were characterized to understand the spectral, mineralogical, and chemical trends in alteration as sensed by multiple techniques. In this work, multiple methods-VSWIR spectroscopy, X-ray diffraction (XRD), and chemical analyses-were used to study a suite of alkaline basalts from San Carlos, Arizona, which have been altered by water in an oxidative, semi-arid environment. Analyses at Gusev Crater by the Spirit rover and Gale Crater by the Curiosity rover have discovered alkaline basaltic rocks. The discovery of Fe, Mg, and Al phyllosilicates on Mars using visible and short-wave infrared (VSWIR) spectroscopy from orbit indicates aqueous alteration of basaltic rocks.
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