An interesting Mars-related paper was just published online in the December 2006 issue of Geosphere. And I believe that GSA (currently) offers Geosphere as an open-access journal (i.e., available to non-subscribers).

Iron isotopes constrain the pathways and formation mechanisms of terrestrial oxide concretions: A tool for tracing iron cycling on Mars?
M.A. Chan, et al.
Geosphere 2, 324–332 (2006)
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