Hibonite

{{Short description|Mineral}}

{{Infobox mineral

| name = Hibonite

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| image = Hibonite - Esiva eluvials, Tulear Province, Madagascar.jpg

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| caption = Hibonite, {{cvt|1.6|cm}} sharp and lustrous crystal from Esiva eluvials, Maromby Commune, Amboasary District, Anosy (Fort Dauphin) Region, Tuléar (Toliara) Province, Madagascar

| category = Oxide minerals

| formula = {{chem2|(Ca,Ce)(Al,Ti,Mg)12O19}}

| IMAsymbol = Hbn{{Cite journal|last=Warr|first=L.N.|date=2021|title=IMA–CNMNC approved mineral symbols|url=https://www.cambridge.org/core/journals/mineralogical-magazine/article/imacnmnc-approved-mineral-symbols/62311F45ED37831D78603C6E6B25EE0A|journal=Mineralogical Magazine|volume=85|issue=3|pages=291–320|doi=10.1180/mgm.2021.43|bibcode=2021MinM...85..291W|s2cid=235729616|doi-access=free}}

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| strunz = 4.CC.45

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| system = Hexagonal

| class = {{ubl|Dihexagonal dipyramidal (6/mmm)|H-M symbol: (6/m 2/m 2/m)}}

| symmetry = P6{{sub|3}}/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

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| habit = Prismatic platy to steep pyramidal crystals

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| cleavage = {0001} good, {10{{overline|1}}0} parting

| fracture = Subconchoidal

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| mohs = {{frac|7|1|2}}–8

| luster = Vitreous

| streak = reddish brown

| diaphaneity = Semitransparent

| gravity = 3.84

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| opticalprop = Uniaxial (-)

| refractive = n{{sub|ω}} = 1.807(2), n{{sub|ε}} = 1.79(1)

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| pleochroism = O = brownish gray; E = gray

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| references = {{cite web|url=http://rruff.geo.arizona.edu/doclib/hom/hibonite.pdf|title=Handbook of Mineralogy|publisher=}}{{cite web|url=http://www.mindat.org/min-1897.html|title=Hibonite: Hibonite mineral information and data.|website=www.mindat.org}}

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Hibonite is a mineral with the chemical formula {{chem2|(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, {{chem2|(Fe,Mg)Al12O19)}}) an alteration mineral from the Allende meteorite.{{cite web|url=http://rruff.info/ima/|title=IMA Mineral List with Database of Mineral Properties|website=rruff.info}} Hibonites were among the first minerals to form as the disk of gas and dust swirling around the young sun cooled.{{cite web |title=A Year in Review and a Look to the Future |url=https://www.fieldmuseum.org/blog/year-review-and-look-future |publisher=Field Museum of Natural History |access-date=4 December 2021 |date=January 11, 2019}}

A very rare gem, hibonite was discovered in 1953 in Madagascar by Paul Hibon, a French prospector.{{cite web|url=http://www.gemdat.org/gem-1897.html|title=Hibonite gemstone information|website=www.gemdat.org}}