  Previously published observations of 60 externally-polluted white dwarfs show
that none of the stars have accreted from intact refractory-dominated parent
bodies composed mainly of Al, Ca and O, although planetesimals with such a
distinctive composition have been predicted to form. We propose that such
remarkable objects are not detected, by themselves, because, unless they are
scattered outward from their initial orbit, they are engulfed and destroyed
during the star's Asymptotic Giant Branch evolution. As-yet, there is at most
only weak evidence supporting a scenario where the composition of any
extrasolar minor planet can be explained by blending of an outwardly scattered
refractory-dominated planetesimal with an ambient asteroid.
