Hibonite - Encyclopedia

Class : Oxides and hydroxides
Subclass : Oxides
Crystal system : Hexagonal
Chemistry : (Ca,Ce,La)(Al,Ti,Mg)₁₂O₁₉
Rarity : Very rare

Hibonite is a complex and rare oxide of strongly metamorphic rocks (marbles, pyroxenites, granulites) which keeps well in alluvium. It can also be found in certain meteorites. It owes its name to Paul Hibon who discovered the mineral in Madagascar. It forms flattened hexagonal prisms or sharp pyramids of a dark brown to black color. A few atoms of thorium replacing those of cerium sometimes make hibonite a weakly radioactive mineral. It is a mineral exclusively reserved for the collection, even if a few cabochons have been cut.

Hibonite in the World

The finest specimens (4 cm crystals) come from the metamorphic anorthite, spinel, corundum and thorianite limestones of Esira, near Taolagnaro (Madagascar), and the alluviums derived from them. Hibonite is, moreover, an almost exclusively Malagasy mineral, with few deposits existing outside this island : Punalur (India), the granulite complex of Furura (Tanzania) and a few sites in Russia.

Hibonite in France

This mineral is not present in the French underground.

Twinning and special forms

No twin known for this mineral species.

Fakes and scams

No fake recorded for this mineral species.

Hardness : 7.5 to 8
Density : 3.84
Fracture : Sub-conchoidal
Streak : Brown

TP : Opaque
IR : 1.790 to 1.807
Birefringence : 0.017
Optical character : Uniaxial -
Pleochroism : Not visible
Fluorescence : None

Solubility : Sulfuric acid

Magnetism : None
Radioactivity : Very low