| Hibonite | |
|---|---|
Hibonite, 1.6 cm sharp and lustrous crystal from Esiva eluvials, Maromby Commune, Amboasary District, Anosy (Fort Dauphin) Region, Tuléar (Toliara) Province, Madagascar |
|
| General | |
| Category | Oxide minerals |
| Chemical formula | (Ca,Ce)Al12O19 |
| Strunz classification | 04.CC.45 |
| Unit cell | a = 5.56Å, c = 21.89Å |
| Identification | |
| Color | black; black, reddish brown |
| Crystal habit | prismatic - crystals shaped like slender prisms |
| Crystal system | hexagonal |
| Cleavage | {0001} good, {1010} parting |
| Mohs scale hardness | 7½-8 |
| Luster | metallic |
| Streak | reddish brown |
| Diaphaneity | opaque |
| Specific gravity | 3.84 |
Hibonite ((Ca,Ce)Al12O19) is a brownish black mineral with a hardness of 7.5-8.0 and a hexagonal crystal structure. It is rare, but is found in high-grade metamorphic rocks on Madagascar. Some presolar grains in primitive meteorites consist of hibonite. Hibonite also is a common mineral in the Ca-Al-rich inclusions (CAIs) found in some chondritic meteorites.