re: Then maybe they at least have some pieces of Mars on them
A few questions for you Ed.
How are planets formed?
Why does Phobos and Deimos have such low densities?
What would happen to a bunch of small debris in orbit around Mars over a billion years or so?
How did Phobos and Deimos get in to their particular orbits with the rotations they have now?
What are the odds of capture against formation orbital in situ?
BTW, I believe you are wrong about the analyzes of spectra of the first few centimeters of surface material being an indicator of the whole composition of either Moon.
My house is not made up of titanium or zinc even though the top layer of paint is white.