Other
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.p44a..07v&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #P44A-07
Other
3620 Mineral And Crystal Chemistry (1042), 3672 Planetary Mineralogy And Petrology (5410), 3675 Sedimentary Petrology, 5460 Physical Properties Of Materials, 5470 Surface Materials And Properties
Scientific paper
Remote spectral data and surface-measured chemical associations with S indicate widespread distribution of Mg-, Ca-, and Fe-sulfate salts on Mars. These salts are identified at least in part as hydrates, but spectral data and the low temperatures and low pH2O of Mars suggest that hydration states vary with origin, latitude, and exposure history. An understanding of stability limits and dehydration/rehydration rates is vital to understanding occurrences that may be interpreted variously as lacustrine, alteration via groundwater or discharge with evaporation, surface weathering, thermal brine systems, eolian recycling, or others. Different sulfates on Mars have varied susceptibility to desiccation at relatively warm, low-RH conditions or to hydration at cold, high-RH conditions. This variability provides a potent tool for interpreting exposure history. Among Ca-sulfates, gypsum and insoluble anhydrite should be stable and remain, respectively, fully hydrated or water-free at most latitudes and through diurnal and seasonal cycles, but bassanite is more sensitive to transient hydration. Mg-sulfates may have various values of n in the formula MgSO4.nH2O, and rehydration of desiccated forms often produces metastable phases. At low pH2O, unlike Ca- sulfates, amorphous forms appear with low values of n dependent, in part, on temperature. Kieserite resists dehydration but may hydrate in conditions where ice is stable at the surface. Fe-sulfates have more complex dehydration and rehydration properties. Jarosite is very resilient because of the lack of H2O molecules and presence of OH. Other Fe-sulfates are not so durable, e.g., coquimbite (Fe2 (SO4)3.9H2O) has independent H2O and dehydration on heating to 30 °C produces an amorphous product that does not rehydrate. Copiapite is similarly susceptible to dehydration. Modest heating of many H2O-bearing ferric sulfates can be destructive, and degradation can produce both cemented solids and viscous liquids. Sulfate salt associations on Mars provide mineral tools to interpret depositional origins, paleohydrology, and paleoclimatology, but these tools require attention to environments of formation, stability relations, and kinetics of hydration and dehydration.
Bish David L.
Vaniman David T.
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