History of the Apollo 15 yellow impact glass and sample 15426 and 15427

Five fragments of the Apollo yellow impact glass from breccias 15426 and 15427 have been dated by the Ar-39/Ar-40 system using a laser microprobe. These glasses were generated by impact at 3.35 + or -0.05 AE and do not confirm the prediction of 1 AE or less by Delano et al. (1982). Since these glasses were probably produced by an impact into a target of moderate-TiO2 basalts, and the only known flows of such material are younger than the impact event, the target for these glasses must be covered up by later basaltic flows. The average Ar-38-Ar-37 exposure age for these glasses is 274 + or -74 m.y.