| Hibonite | |
| Category: | Oxide minerals |
| Imasymbol: | Hbn[1] |
| Strunz: | 4.CC.45 |
| System: | Hexagonal |
| Symmetry: | P6/mmc |
| Unit Cell: | a = 5.56, c = 21.89 [Å]; Z = 2 |
| Color: | Brownish black to black; reddish brown in thin fragments; blue in meteorite occurrence |
| Habit: | Prismatic platy to steep pyramidal crystals |
| Cleavage: | good, parting |
| Fracture: | Subconchoidal |
| Mohs: | –8 |
| Luster: | Vitreous |
| Streak: | reddish brown |
| Diaphaneity: | Semitransparent |
| Gravity: | 3.84 |
| Opticalprop: | Uniaxial (-) |
| Refractive: | n = 1.807(2), n = 1.79(1) |
| Pleochroism: | O = brownish gray; E = gray |
| References: | [2] [3] |
Hibonite is a mineral with the chemical formula, 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,) 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]
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]