Hibonite, from Madagascar

Hibonite Madagascar

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Hibonite, from Madagascar

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Hibonite ((Ca,Ce)(Al,Ti,Mg)12O19) 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. Hibonite is closely related to hibonite-Fe (IMA 2009-027, ((Fe,Mg)Al12O19)) an alteration mineral from the Allende meteorite.

A very rare gem, Named after Paul Hibon, a french prospector in Madagascar, who discovered the mineral in june 1953. He sent a parcel with some samples to Jean Behier for examination in the same year. Behier recognized it as a possible new mineral and gave it the working name “hibonite”. He forwarded the sample to C. Guillemin, Labratoire de Minéralogie de la Sorbonne, in Paris, France to be further analyzed. It resulted in a description of the new mineral by Curien et al (1956).

Hibonite from Esiva, Fort Dauphin region, Tuléar, Madagascar
Black, hard crystals suspended in metamorphosed limestone matrix rich in calcic palgioclase. Probable associates within the matrix are corundum, spinel and thorianite. Described in 1956. Not to be confused with Hibbenite. Hibonite is named after P. Hibon, who discovered the mineral.

General

Category: Oxide minerals
Formula: (Ca,Ce)(Al,Ti,Mg)12O19
Crystal system: Hexagonal
Crystal class: Dihexagonal dipyramidal (6/mmm)
H-M symbol: (6/m 2/m 2/m)

Identification

Color: Brownish black to black; reddish brown in thin fragments; blue in meteorite occurrence
Crystal habit: Prismatic platy to steep pyramidal crystals
Cleavage: {0001} good, {1010} parting
Fracture: Subconchoidal
Mohs scale hardness: 7½-8
Luster: Vitreous
Streak: reddish brown
Diaphaneity: Semitransparent
Specific gravity: 3.84
Optical properties: Uniaxial (-)
Refractive index: nω = 1.807(2), nε = 1.79(1)
Pleochroism: O = brownish gray; E = gray

Hibonite, from Madagascar

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