Nioboholtite

{{infobox mineral

| name = Nioboholtite

| category = Silicate mineral

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| formula = (Nb_0.6[]_0.4)Al₆BSi₃O₁₈

| IMAsymbol = Nhlt{{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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| system = Orthorhombic

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

| symmetry = Pnma

| unit cell = a = 47.00, b = 11.83
c = 20.24 [Å] (approximated)

| color = Creamy-white to brownish yellow, grey-yellow

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| streak = White

| diaphaneity = Translucent

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| opticalprop = Biaxal (-)

| refractive = nα=1.74-1.75, nβ~1.76, nγ~1.76 (approximated)

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| references ={{cite journal|doi=10.1180/minmag.2013.077.6.10 |title=The dumortierite supergroup. II. Three new minerals from the Szklary pegmatite, SW Poland: Nioboholtite, (Nb_0.6〈_0.4)Al₆BSi₃O₁₈, titanoholtite, (Ti_0.75〈_0.25)Al₆BSi₃O₁₈, and szklaryite, 〈Al₆BAs³⁺₃O₁₅ |journal=Mineralogical Magazine |volume=77 |issue=6 |pages=2841 |year=2013 |last1=Pieczka |first1=A. |last2=Evans |first2=R. J. |last3=Grew |first3=E. S. |last4=Groat |first4=L. A. |last5=Ma |first5=C. |last6=Rossman |first6=G. R. |bibcode=2013MinM...77.2841P |s2cid=51740732 |url=https://authors.library.caltech.edu/41877/1/s10.pdf }}{{cite web|url=http://www.mindat.org/min-43588.html |title=Nioboholtite: Nioboholtite mineral information and data |website=Mindat.org |accessdate=2016-03-03}}

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Nioboholtite is an extremely rare mineral with the formula (Nb_0.6[]_0.4)Al₆BSi₃O₁₈. It is the niobium-rich member of the dumortierite supergroup, and the niobium analogue of holtite of the holtite group. It is one of three quite recently found minerals of this group, the other two being titanoholtite and szklaryite, all coming from the Szklary village near Ząbkowice Śląskie in Poland. They occur in a unique pegmatite. Nioboholtite and schiavinatoite are both minerals with essential niobium and boron.{{cite web|url=http://www.mindat.org/min-7110.html |title=Schiavinatoite: Schiavinatoite mineral information and data |website=Mindat.org |accessdate=2016-03-10}}