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Mineral From Wikipedia, the free encyclopedia
Hibonite is a mineral with the chemical formula (Ca,Ce)(Al,Ti,Mg)12O19, occurring in various colours, 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 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.[4] Hibonites were among the first minerals to form as the disk of gas and dust swirling around the young sun cooled.[5]
Hibonite | |
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![]() Hibonite, 1.6 cm (0.63 in) sharp and lustrous crystal from Esiva eluvials, Maromby Commune, Amboasary District, Anosy (Fort Dauphin) Region, Tuléar (Toliara) Province, Madagascar | |
General | |
Category | Oxide minerals |
Formula (repeating unit) | (Ca,Ce)(Al,Ti,Mg)12O19 |
IMA symbol | Hbn[1] |
Strunz classification | 4.CC.45 |
Crystal system | Hexagonal |
Crystal class |
|
Space group | P63/mmc |
Unit cell | a = 5.56, c = 21.89 [Å]; Z = 2 |
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 | 7+1⁄2–8 |
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 |
References | [2][3] |
A very rare gem, hibonite was discovered in 1953 in Madagascar by Paul Hibon, a French prospector.[6]
Hibonite can vary in colour, from a bright blue, to green, to orange, to a nearly black deep brown. The colour is related to the degree of oxidation; meteoritic hibonite tends to be blue.[7]
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