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Mineralogy of the Paso Robles soils on Mars

Melissa D. Lane^1,*, Janice L. Bishop², M. Darby Dyar³, Penelope L. King^4,, Mario Parente⁵ and Brendt C. Hyde⁴

¹ Planetary Science Institute, Tucson, Arizona 85719, U.S.A.
² SETI Institute/NASA-Ames Research Center, Mountain View, California 94043, U.S.A.
³ Mount Holyoke College, South Hadley, Massachusetts 01075, U.S.A.
⁴ University of Western Ontario, London, Ontario N6A 5B7, Canada
⁵ Stanford University, Stanford, California 94305, U.S.A.

Correspondence: ^* E-mail: lane{at}psi.edu

Visible, near-infrared, thermal, and Mössbauer spectroscopic data from the exposed, bright track soil at the "Paso Robles" site within Gusev crater, Mars, indicate the presence of Fe³⁺-sulfates and possibly Fe³⁺-phosphates admixed with the host soil. When the spectroscopic analyses are combined with constraints imposed by chemical data, the determined dominant Fe³⁺-sulfate component is hydrous, and all of the spectroscopic methods suggest that it is probably ferricopiapite or some closely related, structurally similar species, possibly mixed with other Fe³⁺ sulfates such as butlerite or parabutlerite, or perhaps (para)coquimbite, fibroferrite, or metahohmanite. Such an assemblage is consistent with formation in a highly oxidized, relatively dehydrated environment with the bulk-sulfate assemblage having OH/(OH + 2SO₄) of < ~0.4. Some Fe³⁺ is likely to be associated with phosphates in the soil in the form of ferristrunzite or strengite.

Key Words: Mars • spectroscopy • sulfate • phosphate • mineralogy • spectra • Paso Robles • acid