The petrology of chondrules in the sharps meteorite

Correlated petrographic and microprobe studies of 96 chondrules in the Sharps (H-3) chondrite indicate that chondritic material had a highly varied pre-accumulation history. Some chondrules, chiefly excentroradial and barred types, appear to be quenched droplets. Others, including most of the metal poor microporphyritic type, appear to have crystallized more slowly and are thought to be fragments of pre-existing rock. Although chondrules of all types show various effects similar to those produced by shock, such effects are most conspicuous in metal-rich chondrules and least conspicuous in spherical chondrules. It is concluded that shock was involved in the origin of chondrules and not simply a secondary effect.It is proposed that chondrules were formed by shock processes during the accumulation of nebular dust into asteroid-sized bodies. Olivine-rich microporphyritic chondrules are thought to be due to complete melting of large masses of target material; metal-rich chondrules represent shock melting and partial vaporization; and spherical, pyroxene-rich chondrules are interpreted as condensates from shock-generated vapor.