kornerupine

{{Infobox mineral

| name = Kornerupine

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| image = Kornerupine-162065.jpg

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| category = Borosilicates

| formula = {{chem2|(Mg,Fe(2+))4(Al,Fe(3+))6(SiO4,BO4)5(O,OH)2}}

| IMAsymbol = Krn{{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}}

| molweight =

| strunz = 9.BJ.50 (10 ed)
VIII/B.31-10 (8 ed)

| dana = 58.01.01.01

| system = Orthorhombic

| class = Dipyramidal (mmm)
H-M symbol: (2/m 2/m 2/m)

| symmetry = Cmcm

| unit cell = a = 15.99, b = 13.7, c = 6.7 [Å]; Z = 4

| color = Colorless, white, grey, greenish, bluish, brown, black

| habit = Prismatic crystals, radiating, massive, fibrous

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| cleavage = Good on {110}

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| mohs = 6 to 7

| luster = Vitreous

| streak = White

| diaphaneity = Transparent to translucent and opaque

| gravity = 3.29–3.35

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| opticalprop = Biaxial (−)

| refractive = n_α = 1.660 – 1.671 n_β = 1.673 – 1.683 n_γ = 1.674 – 1.684

| birefringence = δ = 0.014

| pleochroism = X = colorless to green; Y = colorless, pale brownish yellow, pale yellowish green; Z = pale brownish green, green, light amber

| 2V = Measured: 3° to 48°

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| references = [http://rruff.geo.arizona.edu/doclib/hom/kornerupine.pdf Mineral data publishing 2001 (PDF)][http://webmineral.com/data/Kornerupine.shtml Webmineral data][http://www.mindat.org/min-2254.html Mindat with locality data]

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Kornerupine (also called Prismatine) is a rare boro-silicate mineral with the chemical formula {{chem2|(Mg,Fe(2+))4(Al,Fe(3+))6(SiO4,BO4)5(O,OH)2}}. It crystallizes in the orthorhombic – dipyramidal crystal system as brown, green, yellow to colorless slender tourmaline like prisms or in massive fibrous forms. It has a Mohs hardness of 7 and a specific gravity of 3.3 to 3.34. Its indices of refraction are nα=1.660 – 1.671, nβ=1.673 – 1.683 and nγ=1.674 – 1.684.

It occurs in boron-rich volcanic and sedimentary rocks which have undergone high grade metamorphism. It is also found in metamorphosed anorthosite complexes.

Kornerupine is valued as a gemstone when it is found in translucent green to yellow shades. The emerald green varieties are especially sought after. It forms a solid solution series with prismatine. Strongly pleochroic, it appears green or reddish brown when viewed from different directions. It has a vitreous luster.

It was first described in 1884 for an occurrence in Fiskernæs in southwest Greenland. It was named in honor of the Danish geologist {{ill|Andreas Nikolaus Kornerup|lt=Andreas Kornerup|de|Andreas Kornerup}} (1857–1881). Although kornerupine was named in 1884, it was not until 1912 that gem-quality material was found and it remains uncommon to this day.

Deposits are found in Burma (Myanmar), Canada (Quebec), Kenya, Madagascar, Sri Lanka, Tanzania, and South Africa.