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Re: Extra-solar material - comets

A few comments on this thread:

1) The SI sample of "stardust" is from Allende.

2) The diamonds in ureilites are not interstellar grains.

3) Pigeonite is a form of pyroxene, not carbon.

4) Interstellar grains, including not just diamonds, but also
   silicon carbide, corundum, graphite, and others, have been found 
   in many primitive chondrites, including at least the CV, CM, CI, 
   H, L, LL, and EH groups.  They are ubiquitous.  Not all formed in
   supernovae. Many grains formed in red giants and other exotic 
   stars.  All are identified by their bizarre isotope ratios for 
   elements like H, C, O, Si, and noble gases.  It's also worth 
   remembering that there may be many interstellar grains that we 
   don't yet see because they have more "normal" isotopic compositions.
   It also has not yet proven possible to search for interstellar
   grains among the common meteoritic minerals because of the very
   difficult searching methods people use; that's why they concentrate
   on highly resistant (chemically and thermally) minerals that
   are the most likely to be survivors of processing in the early 
   solar nebula.

jeff