Clark BC, Arvidson RE, Gellert R, Morris RV, Ming DW, Richter L, Ruff SW, Michalski JR, Farrand WH, Yen AS, Herkenhoff KE, Li R, Squyres SW, Schröder C, Klingelhoefer G & Bell III JF (2007) Evidence for montmorillonite or its compositional equivalent in Columbia Hills, Mars. Journal of Geophysical Research: Planets, 112 (E6), Art. No.: E06S01. https://doi.org/10.1029/2006JE002756
During its exploration of the Columbia Hills, the Mars Exploration Rover ‘‘Spirit’’ encountered several similar samples that are distinctly different from Martian meteorites and known Gusev crater soils, rocks, and sediments. Occurring in a variety of contexts and locations, these ‘‘Independence class’’ samples are rough-textured, iron-poor (equivalent FeO 4 wt%), have high Al/Si ratios, and often contain unexpectedly high concentrations of one or more minor or trace elements (including Cr, Ni, Cu, Sr, and Y). Apart from accessory minerals, the major component common to these samples has a compositional profile of major and minor elements which is similar to the smectite montmorillonite, implicating this mineral, or its compositional equivalent. Infrared thermal emission spectra do not indicate the presence of crystalline smectite. One of these samples was found spatially associated with a ferric sulfate-enriched soil horizon, possibly indicating a genetic relationship between these disparate types of materials. Compared to the nearby Wishstone and Watchtower class rocks, major aqueous alteration involving mineral dissolution and mobilization with consequent depletions of certain elements is implied for this setting and may be undetectable by remote sensing from orbit because of the small scale of the occurrences and obscuration by mantling with soil and dust.
Journal of Geophysical Research: Planets: Volume 112, Issue E6