Hibonite: Properties and Occurrences

Hibonite [(Ca, Ce)(Al, Ti, Mg)12O19] is a very rare gem. It is a calcium aluminate mineral found in carbonaceous chondrite meteorites. Stones which are large enough or transparent enough for faceting are very sparse. It is named after Paul Hibon, a French prospector who discovered the mineral in Madagascar.

A very rare gem, Hibonite was discovered in Madagascar by Paul Hibon, a French prospector. It is slightly radioactive.

General Information

  • Category: Oxide minerals
  • Formula: [(Ca, Ce)(Al, Ti, Mg)12O19]
  • Crystal system: Hexagonal
  • Crystal class: Dihexagonal dipyramidal (6/mmm)

Fig: Hibonite

Properties

Hibonite 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.

  • Color: Brownish black to black; reddish brown in thin fragments; blue in meteorite occurrence
  • Crystal habit: Prismatic platy to steep pyramidal crystals
  • Fracture: Subconchoidal
  • Mohs scale hardness: 7.5 – 8
  • Luster: Vitreous
  • Streak: reddish brown
  • Diaphaneity: Semitransparent
  • Specific gravity: 3.84
  • Optical properties: Uniaxial (-)

Occurrence: In metamorphosed limestone, pyroxenite, gneiss, and granulite of the amphibolites to granulite facies; also alluvial. A common accessory in Ca-Al-rich inclusions in some carbonaceous chondrites.

Hibonite also is a common mineral in the Ca-Al-rich inclusions (CAIs) found in some chondritic meteorites. It is closely related to hibonite-Fe (IMA 2009-027, ((Fe, Mg)Al12O19)) an alteration mineral from the Allende meteorite.

Association: Calcic plagioclase, corundum, spinel, thorianite, titanite (Esiva, Madagascar); anorthite, grossular, titanite, zoisite, clinozoisite (Mahenge, Tanzania); vesuvianite, hercynite, corundum, andalusite, kyanite, diopside, rutile, titanite, magnetite (Shoriya Mountains, Russia).

 

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