The clays on Mars.
Clays have recently been detected on Mars, and on the *surface* :
COMPOSITIONAL MAPPING WITH TES IN VALLES MARINERIS, MARS.
L. R. Gaddis, M. I. Staid, and T. N. Titus,
Astrogeology Program, U.S. Geological Survey, Flagstaff, AZ, lgaddis@usgs.gov.
"Demixing results also indicate the presence
of iron-rich materials within the canyon including
gray hematite and the clay minerals (sheet silicates)
nontronite and Fe-smectite."
http://emma.la.asu.edu/TESworkshop/gaddis_abs.pdf
Bob Clark