Hibonite

Hibonite
Hibonite, 1.6 cm 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
Strunz classification 4.CC.45
Crystal system Hexagonal
Crystal class Dihexagonal dipyramidal (6/mmm)
H-M symbol: (6/m 2/m 2/m)
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 [1][2]

Hibonite ((Ca,Ce)(Al,Ti,Mg)12O19) is a mineral, 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 (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.[3]

A very rare gem, hibonite was discovered in 1953 in Madagascar by Paul Hibon, a French prospector.[4]

Colour

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.[5]

See also

References

  1. ↑ "Handbook of Mineralogy" (PDF).
  2. ↑ "Hibonite: Hibonite mineral information and data". www.mindat.org.
  3. ↑ "IMA Mineral List with Database of Mineral Properties". rruff.info.
  4. ↑ "Hibonite gemstone information". www.gemdat.org.
  5. ↑ Ihinger, Phillip D.; Stolper, Edward (May 1986). "The color of meteoritic hibonite: an indicator of oxygen fugacity". Earth and Planetary Science Letters. 78 (1): 67–79. doi:10.1016/0012-821X(86)90173-1.


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