Mineral Guide · Mineral

Hibonite

Hibonite is a rare calcium aluminium oxide, valued by collectors and planetary scientists for its refractory chemistry and dark red-brown crystals.

Interactive 3D structure

Crystal structure

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Rotate with the mouse or touch. The cell frame and a, b, c labels show the repeating unit used by the structure model.

Mineral properties

Formula: CaAl₁₂O₁₉
Class: Oxides
Crystal system: Hexagonal
Typical colours: black, brown, red-brown, orange-brown
Lustre: Sub-metallic, Vitreous
Hardness: 7.50-8.00
Specific gravity: 3.80-4.10
Crystal habit: Granular, Prismatic, Tabular
Origin: high-temperature metamorphic rocks, aluminium-rich inclusions and unusual calcium-aluminium-rich assemblages

What is Hibonite?

Hibonite is a rare calcium aluminium oxide, valued by collectors and planetary scientists for its refractory chemistry and dark red-brown crystals.

Mineralogy and structure

Reference formula: CaAl₁₂O₁₉. Hibonite has a hexagonal magnetoplumbite-type structure and commonly contains titanium and rare-earth substitutions. The COD model used here is a compositionally substituted hibonite reference. Hibonite belongs to the oxides and has a hexagonal crystal system. Typical hardness is 7.5–8 on the Mohs scale and specific gravity is approximately 3.8–4.1.

Colour and appearance

Typical colours include brown, red-brown, black, orange-brown. The usual tabular, prismatic, granular habit and vitreous, sub-metallic lustre are useful descriptive features, but colour alone is not diagnostic.

Formation and localities

Hibonite forms in or is associated with high-temperature metamorphic rocks, aluminium-rich inclusions and unusual calcium-aluminium-rich assemblages. Important documented localities include Madagascar, Tanzania, Russia, Canada and rare meteoritic occurrences.

Collecting and care

Protect sharp crystals and retain the locality or analytical record because similar dark oxides can look alike.

Sources and editorial review

Reviewed by NotOnlyRocks Editorial Team

Last reviewed: 31 August 2026

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