Dirty rocks: Thermal infrared studies of dusty, sandy, or coated soils and rocks on Mars and Earth

Crystalline, grey hematite has been identified in Meridiani Planum, the Aram Chaos region, and Valles Marineris on Mars and has been linked to aqueous processes. This study describes hematite concentrations in Valles Marineris. Hematite forms lag deposits associated with sulfate-rich, bright, layered deposits and is mixed with basaltic materials consisting of: 30-45% pyroxene, 15-20% plagioclase, 5-10% olivine, 5-20% glass or phyllosilicates, 5-25% sulfates, and 0-20% carbonates. The hematite spectral shape is consistent with that derived from other sites, indicating global similarities in formation. Layered deposits likely formed when groundwater upwellings within Valles Marineris troughs interacted with atmospheric volcanic gasses to produce acidic waters. Surface waters acted to trap basaltic particulates that were cemented with sulfates. Syn-or post-depositional low temperature hydrothermal alteration in near neutral pH water converted iron sulfates to goethite which were later altered to hematite.; The particulate fraction of the regolith (soil) at Gusev Crater, Mars was examined with the Miniature Thermal Emission Spectrometer (Mini-TES), part of the Mars Exploration Rover (MER) 'Spirit' mission. Fifty-two soil observations from sols 1 through 404 indicate three soil components: (1) bright, very fine-grained dust, (2) dark, fine-grained, basaltic sand, and (3) bright, Ca-rich, hydrated sulfate. Dust was identified as the fraction with globally homogenous characteristics. The basaltic sand is homogenous from the landing site to the Columbia Hills and has a modal mineralogy of: 40-45% plagioclase, 20-35% pyroxene, 10-15% olivine, <10% sulfate, and <10% glass or sheet silicates. Soils are regionally homogenous with no compositional variation related to local rock composition.; A study of the Painted Rocks Mountains, near Gila Bend, AZ was performed using multispectral airborne and orbital data. Thermal Imaging Multispectral Scanner (TIMS) and Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) thermal infrared image data were deconvolved using data derived from images, laboratory measurements of rock samples, and field spectrometer measurements. Caliche, dust, vegetation, and rock coatings affected detection of rock composition and the ability of the multispectral dataset to discriminate between compositionally similar rock units. Basalts, andesites, and dacites were accurately discriminated in image data and mineral variations of ∼10% were detected.