Mg Isotopic studies of Leoville "compact" type a CAI

One long-standing problem in the application of Al-Mg isotopic systematics to the chronology of CAI is the enigmatic Mg isotopic record of hibonite. Hibonite (ideally, CaAI_(12)O_(19)) is one of the first major element bearing phases to appear in the condensation sequence [1] and occurs as a major constituent only in CAI whose bulk composition is considerably more refractory than Allende Type Bl CAI.