QUESTION:
Based on the APXS results, what is the major element (SiO2, Al2O3, Fe2O3,
etc.) composition of a Martian rock such as Barnacle Bill?  (Any chance of
posting geochemical results from the APXS on the MPF website so the public
can compare compositions with terrestrial rocks?)

ANSWER from Jeff Plescia on July 14, 1997:
The total APX spectra has not yet been released.  The data indicate that the
bulk composition of the rock, Barnacle Bill, is similar to that of an
andesite.  However, the claim has yet to be made that it is an andesite.

You can check the results when they are released on the Pathfinder
web page:  http://mpfwww.arc.nasa.gov.  Pick a mirror site there.

ANSWER from Ted Roush on July 11, 1997:
Barnacles are just a loose descriptive term and was never intended to imply
actual barnacles.  These areas on the rock probably represent material that
is more resistive to erosion (wind or water) than surrounding material. 
They could be different minerals than those that compose the rest of the
rock. They could be different rocks that have been incorporated into the
larger rock (geologists call this type of rock a conglomerate). Hopefully,
additional analysis of spectral imaging data will more clearly define what
these features are.