QUESTION:
Are the rocks you examine on Mars made of true Martian material or are they
pieces of the many meteorites that have hit Mars over the eons?

ANSWER from Mike Mellon on August 10, 1997:
Certainly some of the surface material on Mars is meteoric in origin, since
the planet is covered with impact craters. However, most of the rocks
scattered by an impact are locally excavated from the crater. Statistically,
it is unlikely to pick a rock at random and find it is not from Mars. It is
important, though, to examine many rocks on Mars to avoid finding ONLY that
one "odd ball" rock that puts us on the wrong track.

Mike Mellon