QUESTION:
Why was only one chemical analysis was made on Barnicle Bill? Wouldn't a
second (or more) chemical analysis on a different part of the Martian rocks
lend information on rock homogeneity to indicate whether the rock is fine or
coarse grained? I understand rock reflectance results have been used to
indicate homogeneity, but why not a second method to confirm the result?

ANSWER from Mike Mellon on August 24, 1997:
Yes, more that one APXS analysis of "Barnacle Bill" would be useful in
determining homogeneity of the rock chemistry. However, within the mission
life time and the life time of the APXS instrument, only a finite number of
analyses can be completed. One of the Mars Pathfinder science objectives is
to analyze many different rocks from many different locations on Mars. This
objective was a driver for choosing the Ares Valles landing site.

At the Ares Valles location it was expected that the catastrophic outflow
would deposit rocks as the flow slowed, debouching into the Chryse Planitia
(a region of Mars). These rocks would have been scoured from a variety of
geologic units, of a variety of ages, from upstream of the flood.  Analyses
of these rocks are expected to provide clues about the geochemical history
of the Martian crust and address basic questions about crustal
differentiation and chemical weathering. Therefore, it is better to have
single analyses of many rocks, than many analyses of a single rock. 
However, I expect that as the mission continues and the spacecraft remains
in good health, some rocks may be reanalyzed.

Mike Mellon