THE FORMATION OF CHONDRULES - PETROLOGIC TESTS OF THE SHOCK-WAVE MODEL

Chondrules are millimeter-sized rounded igneous rocks within chondriti c meteorites, Their textures and fractionated mineral chemistries sugg est that they formed by repeated, localized, brief (minutes to hours) melting of cold aggregates of mineral dust in the protoplanetary nebul a, Astrophysical models of chondrule formation have been unable to exp lain the petrologically diverse nature oi chondrites. However, a nebul ar shock wave model for chondrule formation agrees with many of the ob served petrologic and geochemical properties of chondrules and shows h ow particles within the nebula are sorted by size and how rims around chondrules are formed. It also explains the volatile-rich nature oi ch ondrule rims and the chondrite matrix.