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  • Other Sources  (26)
  • 1990-1994  (18)
  • 1985-1989  (8)
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  • 1990-1994  (18)
  • 1985-1989  (8)
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  • 1
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    Weathering of sulfides on Mars (1987)
    In:  CASI
    Details
    Publication Date: 2013-08-29
    Description: Pyrrhotite-pentlandite assemblages in mafic and ultramafic igneous rocks may have contributed significantly to the chemical weathering reactions that produce degradation products in the Martian regolith. By analogy and terrestrial processes, a model is proposed whereby supergene alteration of these primary Fe-Ni sulfides on Mars has generated secondary sulfides (e.g., pyrite) below the water table and produced acidic groundwater containing high concentrations of dissolved Fe, Ni, and sulfate ions. The low pH solutions also initiated weathering reactions of igneous feldspars and ferromagnesian silicates to form clay silicate and ferric oxyhydroxide phases. Near-surface oxidation and hydrolysis of ferric sulfato-and hydroxo-complex ions and sols formed gossan above the water table consisting of poorly crystalline hydrated ferric sulfates (e.g., jarosite), oxides (ferrihydrite, goethite), and silica (opal). Underlying groundwater, now permafrost contains hydroxo sulfato complexes of Fe, Al, Mg, Ni, which may be stabilized in frozen acidic solutions beneath the surface of Mars. Sublimation of permafrost may replenish colloidal ferric oxides, sulfates, and phyllosilicates during dust storms on Mars.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar and Planetary Inst., MEVTV Workshop on Nature and Composition of Surface Units on Mars; p 34-36
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  • 2
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    Sulfide mineralization: Its role in chemical weathering of Mars (1988)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Pyrrhotite-pentlandite assemblages in mafic and ultramafic igneous rocks may have contributed significantly to the chemical weathering reactions that produced degradation products in the Martian regolith. By analogy with terrestrial processes, a model is proposed whereby supergene alteration of these primary Fe-Ni sulfides on Mars has generated secondary sulfides (e.g., pyrite) below the water table and produced acidic groundwater containing high concentrations of dissolved Fe, Ni and sulfate ions. The low pH solutions also initiated weathering reactions of igneous feldspars and ferromagnesian silicates to form clay silicate and ferric oxyhydroxide phases. Near-surface oxidation and hydrolysis of ferric sulfato- and hydroxo-complex ions and sols formed gossans above the water table consisting of poorly crystalline hydrated ferric sulfates (e.g., jarosite), oxides (ferrihydrite, goethite) and silica (opal). Underlying groundwater, now permafrost, contains hydroxo sulfato complexes of Fe, Al, Mg, Ni, etc., which may be stabilized in frozen acidic solutions beneath the surface of Mars. Sublimation of permafrost may replenish colloidal ferric oxides, sulfates and phyllosilicates during dust storms on Mars.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar and Planetary Inst., Workshop on Mars Sample Return Science; p 48-50
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  • 3
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    Sampling the oxidative weathering products and the potentially acidic permafrost on Mars (1988)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Large areas of Mars' surface are covered by oxidative weathering products containing ferric and sulfate ions having analogies to terrestrial gossans derived from sulfide mineralization associated with iron-rich basalts. Chemical weathering of such massive and disseminated pyrrhotite-pentlandite assemblages and host basaltic rocks in the Martian environment could have produced metastable gossaniferous phases (limonite containing poorly crystalline hydrated ferric sulfates and oxyhydroxides, clay silicates and opal). Underlying groundwater, now permafrost on Mars, may still be acidic due to incomplete buffering reactions by wall-rock alteration of unfractured host rock. Such acidic solutions stabilize temperature-sensitive complex ions and sols which flocculate to colloidal precipitates at elevated temperatures. Sampling procedures of Martian regolith will need to be designed bearing in mind that the frozen permafrost may be corrosive and be stabilizing unique complex ions and sols of Fe, Al, Mg, Ni and other minor elements.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar and Planetary Inst., Workshop on Mars Sample Return Science; p 46-47
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  • 4
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    Gossans on Mars: Spectral features attributed to jarosite (1987)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Jarosites, which are present in terrestrial gossans capping oxidized sulfides associated with mafic igneous rocks, may also be present in Martian regolith. Spectral characteristics of jarosites are displayed in remote sensed reflectance spectra of bright regions of Mars surface. The occurrence of jarosite in the regolith would imply that acidic permafrost and sulfide ores exist beneath the surface of Mars.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA, Washington, Reports of Planetary Geology and Geophysics Program, 1986; p 176-177
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  • 5
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    Hisingerite and iddingsite on Mars: Degradation of iron-rich basalts (1987)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Paragenetic evidence that indicates that hisingerite may have formed during the evolution of Martian regolith is summarized. Hisingerite was once regarded as poorly crystalline iron-rich smectite or nontronite. However, recent electron microscopy and X-ray studies have revealed hisingerite to have an amorphous or gel structure containing a disordered array of (FeO6) octahedra and (SiO4) tetrahedra. It is just this coordination environment and degree of crystallinity that matches materials simulating the spectral properties of the bright regions of Mars. Therefore, hisingerite and basic ferric sulfate minerals appear to be major contributers to remote sensed reflectance spectral profiles of Mars.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA, Washington, Reports of Planetary Geology and Geophysics Program, 1986; p 175
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  • 6
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    Rates of oxidative weathering on the surface of Mars (1992)
    In:  CASI
    Details
    Publication Date: 2013-08-29
    Description: Implicit in the mnemonic 'MSATT' (Mars surface and atmosphere through time) is that rates of surface processes on Mars through time should be investigated, including studies of the kinetics and mechanism of oxidative weathering reactions occurring in the Martian regolith. Such measurements are described. Two major elements analyzed in the Viking Lander XRF experiment that are most vulnerable to atmospheric oxidation are iron and sulfur. Originally, they occurred as Fe(2+)-bearing silicate and sulfide minerals in basaltic rocks on the surface of Mars. However, chemical weathering reactions through time have produced ferric- and sulfate-bearing assemblages now visible in the Martian regolith. Such observations raise several question about: (1) when the oxidative weathering reactions took place on Mars; (2) whether or not the oxidized regolith is a fossilized remnant of past weathering processes; (3) deducting chemical interactions of the ancient Martian atmosphere with its surface from surviving phases; (4) possible weathering reactions still occurring in the frozen regolith; and (5) the kinetics and mechanism of past and present-day oxidative reactions on Mars. These questions may be addressed experimentally by studying reaction rates of dissolution and oxidation of basaltic minerals, and by identifying reaction products forming on the mineral surfaces. Results for the oxidation of pyrrhotite and dissolved ferrous iron are reported.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar and Planetary Inst., Workshop on the Martian Surface and Atmosphere Through Time; p 26-27
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  • 7
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    Oxygen in the Martian atmosphere: Regulation of PO2 by the deposition of iron formations on Mars (1992)
    In:  CASI
    Details
    Publication Date: 2013-08-29
    Description: During Earth's early history, and prior to the evolution of its present day oxygenated atmosphere, extensive iron rich siliceous sedimentary rocks were deposited, consisting of alternating layers of silica (chert) and iron oxide minerals (hematite and magnetite). The banding in iron formations recorded changes of atmosphere-hydrosphere interactions near sea level in the ancient ocean, which induced the oxidation of dissolved ferrous iron, precipitation of insoluble ferric oxides and silica, and regulation of oxygen in Earth's early atmosphere. Similarities between the Archean Earth and the composition of the present day atmosphere on Mars, together with the pervasive presence of ferric oxides in the Martian regolith suggest that iron formation might also have been deposited on Mars and influenced the oxygen content of the Martian atmosphere. Such a possibility is discussed here with a view to assessing whether the oxygen content of the Martian atmosphere has been regulated by the chemical precipitation of iron formations on Mars.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar and Planetary Inst., Papers Presented to the Workshop on the Evolution of the Martian Atmosphere; p 3-5
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  • 8
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    The fate of iron on Mars: Mechanism of oxidation of basaltic minerals to ferric-bearing assemblages (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-01-25
    Description: Perhaps the most conspicuous indication that chemical weathering has occurred on the surface of Mars is the overall color of the red planet and the spectroscopic features that identify ferric-bearing assemblages in the martian regolith. Apparently, Fe(2+) ions in primary minerals in parent igneous rocks on the martian surface have been oxidized to ferric iron, which occurs in degradation products that now constitute the regolith. The mineralogy of the unweathered igneous rocks prior to weathering on the martian surface is reasonably well constrained, mainly as a result of petrographic studies of the SNC meteorites. However, the alteration products resulting from oxidative weathering of these rocks are less well-constrained. The topics covered include the following: primary rocks subjected to chemical weathering; dissolution processes; oxidation of dissolved Fe(2+); mechanism of polymerization of hydrous ferric oxides; terrestrial occurrences of ferromagnesian smectites; and dehydroxylated Mg-Fe smectites on Mars.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar and Planetary Inst., MSATT Workshop on Chemical Weathering on Mars; p 8-9
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  • 9
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    Venus mountain-top mineralogy: Misconceptions about pyrite as the high radar-reflecting phase (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-01-25
    Description: Altitude-dependent, high radar-reflectivity surfaces on Venus are observed on most mountainous volcanic terranes above a planetary radius of about 6054 km. However, high radar-reflectivity areas also occur at lower altitudes in some impact craters and plain terranes. Pyrite (FeS2) is commonly believed to be responsible for the high radar reflectivities at high elevations on Venus, on account of large dielectric constants measured for sulfide-bearing rocks that were erroneously attributed to pyrite instead of pyrrhotite. Pentlandite-pyrrhotite assemblages may be responsible for high reflectivities associated with impact craters on the Venusian surface, by analogy with Fe-Ni sulfide deposits occurring in terrestrial astroblemes. Mixed-valence Fe(2+)-Fe(3+) silicates, including oxyhornblende, oxybiotite, and ilvaite, may contribute to high radar reflecting surfaces on mountain-tops of Venus.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar and Planetary Inst., Twenty-fourth Lunar and Planetary Science Conference. Part 1: A-F; p 233-234
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  • 10
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    Dehydroxylated clay silicates on Mars: Riddles about the Martian regolith solved with ferrian saponites (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-01-25
    Description: Clay silicates, resulting from the chemical weathering of volcanic glasses and basaltic rocks of Mars, are generally believed to be major constituents of the martian regolith and atmospheric dust. Because little attention has been given to the role, if any, of Mg-bearing clay silicates on the martian surface, the crystal chemistry, stability, and reactivity of Mg-Fe smectites are examined. Partially dehydroxylated ferrian saponites are suggested to be major constituents of the surface of Mars, regulating several properties of the regolith.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar and Planetary Inst., MSATT Workshop on Chemical Weathering on Mars; p 6-7
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