Nioboholtite

Nioboholtite
General
Category Silicate mineral
Formula
(repeating unit)		 (Nb0.6[]0.4)Al6BSi3O18
Crystal system Orthorhombic, Pbcm
Unit cell a=47.00, b=11.83, c=20.24 [Å] (approximated)
Identification
Color Creamy-white to brownish yellow, grey-yellow
Crystal symmetry Orthorhombic – Dipyramidal (mmm)
Streak White
Diaphaneity Translucent
Optical properties Biaxal (-)
Refractive index nα=1.74-1.75, nβ~1.76, nγ~1.76 (approximated)
References [1][2]

Nioboholtite is an extremely rare mineral with the formula (Nb0.6[]0.4)Al6BSi3O18. It is niobium-rich member of dumortierite supergroup, and 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.[1] Nioboholtite and schiavinatoite are both minerals with essential niobium and boron.[3]

Association

Nioboholtite is mainly associated with holtite and a number of other minerals (see szklaryite).[1]

Notes on chemistry

Main impurities in nioboholtite are antimony and arsenic, with trace or minor aluminium iron, tantalum, titanium, phosphorus and hydroxyl groups.[1]

References

  1. 1 2 3 4 Pieczka, A.; Evans, R. J.; Grew, E. S.; Groat, L. A.; Ma, C.; Rossman, G. R. (2013). "The dumortierite supergroup. II. Three new minerals from the Szklary pegmatite, SW Poland: Nioboholtite, (Nb0.6〈0.4)Al6BSi3O18, titanoholtite, (Ti0.75〈0.25)Al6BSi3O18, and szklaryite, 〈Al6BAs3+3O15". Mineralogical Magazine 77 (6): 2841. doi:10.1180/minmag.2013.077.6.10.
  2. ↑ "Nioboholtite: Nioboholtite mineral information and data". Mindat.org. Retrieved 2016-03-03.
  3. ↑ "Schiavinatoite: Schiavinatoite mineral information and data". Mindat.org. Retrieved 2016-03-10.


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