Geochemical properties of rocks and soils in Gusev Crater, Mars: Results of the Alpha Particle X-Ray Spectrometer from Cumberland Ridge to Home Plate

Geochemical diversity of rocks and soils has been discovered by the Alpha Particle X-Ray Spectrometer ( APXS) during Spirit's journey over Husband Hill and down into the Inner Basin from sol 470 to 1368. The APXS continues to operate nominally with no changes in calibration or spectral degradation over the course of the mission. Germanium has been added to the Spirit APXS data set with the confirmation that it occurs at elevated levels in many rocks and soils around Home Plate. Twelve new rock classes and two new soil classes have been identified at the Spirit landing site since sol 470 on the basis of the diversity in APXS geochemistry. The new rock classes are Irvine ( alkaline basalt), Independence ( low Fe outcrop), Descartes ( outcrop similar to Independence with higher Fe and Mn), Algonquin ( mafic-ultramafic igneous sequence), Barnhill ( volcaniclastic sediments enriched in Zn, Cl, and Ge), Fuzzy Smith ( high Si and Ti rock), Elizabeth Mahon ( high Si, Ni, and Zn outcrop and rock), Halley ( hematite-rich outcrop and rock), Montalva ( high K, hematite-rich rock), Everett ( high Mg, magnetite-rich rock), Good Question ( high Si, low Mn rock), and Torquas ( high K, Zn, and Ni magnetite-rich rock). New soil classes are Gertrude Weise ( very high Si soil) and Eileen Dean ( high Mg, magnetite-rich soil). Aqueous processes have played a major role in the formation and alteration of rocks and soils on Husband Hill and in the Inner Basin.