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Reflectance spectroscopy of ferric sulfate-bearing montmorillonites as Mars soil analog materialsSpectroscopic analyses have shown that smectites enhanced in the laboratory with additional ferric species exhibit important similarities to those of the soils on Mars. Ferrihydrite in these chemically treated smectites has features in the visible to near-infrared region that resemble the energies and band strengths of features in reflectance spectra observed for several bright regions on Mars. New samples have been prepared with sulfate as well, because S was found by Viking to be a major component in the surface material on Mars. A suite of ferrihydrite-bearing and ferric sulfate-bearing montmorillonites, prepared with variable Fe3+ and S concentrations and variable pH conditions, has been analyzed using reflectance spectroscopy in the visible and infrared regions, Mossbauer spectroscopy at room temperature and 4 K, differential thermal analysis, and X-ray diffraction. These analyses support the formation of ferrihydrite of variable crystallinity in the ferrihydrite-bearing montmorillonites and a combination of schwertmannite and ferrihydrite in the ferric sulfate-bearing montmorillonites. Small quantities of poorly crystalline or nanophase forms of other ferric materials may also be present in these samples. The chemical formation conditions of the ferrihydrite-bearing and ferric sulfate-bearing montmorillonites influence the character of the low temperature Mossbauer sextets and the visible reflectance spectra. An absorption minimum is observed at 0.88-0.89 micrometers in spectra of the ferric sulfate-bearing samples, and at 0.89-0.92 micrometers in spectra of the ferrihydrate-bearing montmorillonites. Mossbauer spectra of the ferric sulfate-bearing montmorillonites indicate variable concentrations of ferrihydrite and schwertmannite in the interlaminar spaces and along grain surfaces. Dehydration under reduced atmospheric pressure conditions induces a greater effect on the adsorbed and interlayer water in ferrihydrite-bearing montmorillonite than on the water in ferric sulfate-bearing montmorillonite. Reflectance spectra of ferric sulfate-bearing montmorillonite include a strong 3-micrometers band that is more resistant to dry atmospheric conditions than the 3-micrometers band in spectra of similarly prepared ferrihydrite-bearing montmorillonites.
Document ID
20040090007
Acquisition Source
Headquarters
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Bishop, J. L.
(Brown University Providence, Rhode Island 02912, United States)
Pieters, C. M.
Burns, R. G.
Edwards, J. O.
Mancinelli, R. L.
Froschl, H.
Date Acquired
August 21, 2013
Publication Date
September 1, 1995
Publication Information
Publication: Icarus
Volume: 117
Issue: 1
ISSN: 0019-1035
Subject Category
Lunar And Planetary Science And Exploration
Funding Number(s)
CONTRACT_GRANT: NAGW-748
CONTRACT_GRANT: NAGW-28
Distribution Limits
Public
Copyright
Other
Keywords
NASA Discipline Exobiology
NASA Center ARC
NASA Program Exobiology
NASA Discipline Number 52-80

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