Mossbauer mineralogy of rock, soil, and dust at Gusev crater, Mars:: Spirit's journey through weakly altered olivine basalt on the plains and pervasively altered basalt in the Columbia Hills -: art. no. E02S13

The Mossbauer spectrometer on Spirit measured the oxidation state of Fe, identified Fe-bearing phases, and measured relative abundances of Fe among those phases for surface materials on the plains and in the Columbia Hills of Gusev crater. Eight Fe-bearing phases were identified: olivine, pyroxene, ilmenite, magnetite, nanophase ferric oxide (npOx), hematite, goethite, and a Fe3+-sulfate. Adirondack basaltic rocks on the plains are nearly unaltered (Fe3+/Fe-T < 0.2) with Fe from olivine, pyroxene ( Ol > Px), and minor npOx and magnetite. Columbia Hills basaltic rocks are nearly unaltered ( Peace and Backstay), moderately altered (WoolyPatch, Wishstone, and Keystone), and pervasively altered ( e. g., Clovis, Uchben, Watchtower, Keel, and Paros with Fe3+/Fe-T similar to 0.6 - 0.9). Fe from pyroxene is greater than Fe from olivine ( Ol sometimes absent), and Fe2+ from Ol + Px is 40 - 49% and 9 - 24% for moderately and pervasively altered materials, respectively. Ilmenite ( Fe from Ilm similar to 3 - 6%) is present in Backstay, Wishstone, Keystone, and related rocks along with magnetite ( Fe from Mt similar to 10 - 15%). Remaining Fe is present as npOx, hematite, and goethite in variable proportions. Clovis has the highest goethite content ( Fe from Gt = 40%). Goethite (alpha-FeOOH) is mineralogical evidence for aqueous processes because it has structural hydroxide and is formed under aqueous conditions. Relatively unaltered basaltic soils (Fe3+/FeT similar to 0.3) occur throughout Gusev crater ( similar to 60 - 80% Fe from Ol + Px, similar to 10 - 30% from npOx, and similar to 10% from Mt). PasoRobles soil in the Columbia Hills has a unique occurrence of high concentrations of Fe3+-sulfate ( similar to 65% of Fe). Magnetite is identified as a strongly magnetic phase in Martian soil and dust.