Oxygen isotopes in chondrule olivine and isolated olivine grains from the CO3 chondrite Allan Hills A77307

— We have measured O‐isotopic ratios in a variety of olivine grains in the CO3 chondrite Allan Hills (ALH) A77307 using secondary ion mass spectrometry in order to study the chondrule formation process and the origin of isolated olivine grains in unequilibrated chondrites. Oxygen‐isotopic ratios of olivines in this chondrite are variable from δ17O = −15.5 to +4.5% and δ18O = −11.5 to +3.9%, with Δ17O varying from −10.4 to +3.5%. Forsteritic olivines, Fa