Journal
AMERICAN MINERALOGIST
Volume 93, Issue 8-9, Pages 1201-1214Publisher
MINERALOGICAL SOC AMER
DOI: 10.2138/am.2008.2737
Keywords
hematite; jarosite; spherule; synthesis; diagenesis; Mars; hydrothermal; concretions; thermal emission spectroscopy; X-ray diffraction; Mossbauer spectroscopy; scanning electron microscopy; transmission electron microscopy
Categories
Funding
- NASA Mars Fundamental Research Program
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We synthesized hematite spherules whose mineralogic, chemical, and crystallographic properties are strikingly similar to those for the hematite-rich spherules in lag deposits oil the surface and embedded ill Outcrops at Meridiani Planum, Mars. The spherules were synthesized in the laboratory along with hydronium jarosite and minor hydronium alunite from Fe-Al-Mg-S-Cl acid-sulfate solutions under hydrothermal conditions. The reaction sequence was (1) precipitation of hydronium jarosite; (2) jarosite dissolution and precipitation of hematite spherules; and (3) precipitation of hydronium alunite upon depletion of hydronium jarosite. The spherules exhibit a radial growth texture with the crystallographic c axis aligned along the radial direction, so that thermal emission spectra have no hematite emissivity minimum at similar to 390 cm(-1). Our experiments show that hydrothermal, acid-sulfate solutions are a pathway for formation of jarosite and the hematite spherules at Meridiani Planum, Mars.
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