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Opaline silica in young deposits on Mars

^{1 1}Jet Propulsion Laboratory/California Institute of Technology, 4800 Oak Grove Drive, Pasadena, California 91109, USA
^{2 2}U.S. Geological Survey, Denver, Colorado 80225, USA
^{3 3}Department of Earth and Planetary Sciences, Washington University, St. Louis, Missouri 63130, USA
^{4 4}SETI Institute/NASA Ames Research Center, Mountain View, California 94043, USA
^{5 5}Department of Geological Sciences, Brown University, Providence, Rhode Island 02912, USA
^{6 6}California Institute of Technology, Pasadena, California 91125, USA
^{7 7}NASA Johnson Space Center, Houston, Texas 77058, USA
^{8 8}Applied Physics Lab, Johns Hopkins University, Laurel, Maryland 20723, USA
^{9 9}Planetary Science Institute, Tucson, Arizona 85719, USA

Correspondence: *E-mail: ralph.milliken{at}jpl.nasa.gov.

High spatial and spectral resolution reflectance data acquired by the Mars Reconnaissance Orbiter Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instrument reveal the presence of H₂O- and SiOH-bearing phases on the Martian surface. The spectra are most consistent with opaline silica and glass altered to various degrees, confirming predictions based on geochemical experiments and models that amorphous silica should be a common weathering product of the basaltic Martian crust. These materials are associated with hydrated Fe sulfates, including H₃O-bearing jarosite, and are found in finely stratified deposits exposed on the floor of and on the plains surrounding the Valles Marineris canyon system. Stratigraphic relationships place the formation age of these deposits in the late Hesperian or possibly the Amazonian, implying that aqueous alteration continued to be an important and regionally extensive process on Mars during that time.

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