Hibonite
Hibonite is a calcium-aluminium oxide among the first minerals to condense in the young Solar System.
Hibonite is a calcium aluminium oxide with small amounts of titanium and magnesium, roughly CaAl12O19. It was described from a deposit in Madagascar, but in meteoritics it is famous for appearing in some of the oldest objects known.
Theory predicts that hibonite is among the first minerals to condense from a cooling gas of solar composition, alongside corundum and perovskite. It is found in calcium-aluminium-rich inclusions in CM chondrites, sometimes as tiny blue crystals or in small spherules. Some hibonite grains carry large isotopic anomalies in calcium and titanium, showing they captured material that had not yet been mixed evenly through the solar nebula.
A few hibonite grains are presolar, made around other stars. Because the mineral is so resistant, it acts as a time capsule for the earliest stage of planet formation, and studies of it have helped show how short-lived radioactive isotopes were spread through the disc.
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