Dear Mike:

I don't know what to make of your plots, as I cannot read them very well

(the JPEG compression produced some fuzzy plots). Anyway, your argument

that the local volcanics do not have the composition of this rock is a

good one. What I would encourage you to do is plot your bulk rock

composition on a Mg/Si versus Al/Si plot, as done in the Rieder et al

paper (Science vol. 278, p 1773, figure 4) and see if it plots on the

Mars trend or the terrestrial trend. I think you had a plot like that,

but I could not read it. Regards, Hap

Harry Y. McSween, Jr.

Department of Geological Sciences

University of Tennessee

Knoxville, TN 37996-1410

tel. (423) 974-9805

fax. (423) 974-2368

email. mcsween@utk.edu