Two interesting papers from the February-March 2006 issue of American Mineralogist:

The Mars/Earth dichotomy in Mg/Si and Al/Si ratios: Is it real?
Justin Filiberto, Hanna Nekvasil, and Donald H. Lindsley
American Mineralogist 91, 471-474 (2006).
Abstract

Application of a new vanadium valence oxybarometer to basaltic glasses from the Earth, Moon, and Mars
Jim M. Karner, Steven R. Sutton, James J. Papike, Charles K. Shearer, John H. Jones, and Matt Newville
American Mineralogist 91, 270-277 (2006).
Abstract