Hibonite
A calcium aluminium oxide, among the very first minerals to condense in the Solar System.
Key facts
- Formula
- CaAl12O19
- Family
- Oxides
- Crystal system
- Hexagonal
What it is
Hibonite is an oxide very rich in aluminium, often with titanium and magnesium. Calculations show it is one of the first minerals to form as a hot gas of solar composition cools, after corundum. It is named after Paul Hibon, who found it in Madagascar.
Where it is found
It occurs as tiny platy crystals in CAIs, especially in CM chondrites such as Murchison, where hibonite-rich inclusions are common. Some of these grains contain no trace of aluminium-26, while others are full of it, suggesting that they formed before the radioactive material was spread through the disc, or in a different region.
How it is recognised
In meteorites it forms blue to colourless hexagonal plates, often only tens of micrometres across. Blue hibonite is coloured by titanium.
Did you know?
Hibonite-rich inclusions in Murchison are sometimes called PLACs, for platy hibonite crystals.
Hibonite in meteorites carries isotope anomalies in calcium and titanium that record material from different stars.