Béhierite

Béhierite is a very rare mineral,[1] a natural tantalum borate of the formula (Ta,Nb)BO4.[3][2] Béhierite is also one of the most simple tantalum minerals. It contains simple tetrahedral borate anions, instead of more common among minerals, planar BO3 groups. It forms a solid solution with its niobium-analogue, schiavinatoite. Both have zircon-type structure (tetragonal, space group I41/amd) and are found in pegmatites.[2] Béhierite and holtite are minerals with essential tantalum and boron.[4]

Béhierite
Béhierite
General
CategoryBorate
Formula
(repeating unit)		(Ta,Nb)BO4
Strunz classification6.AC.15
Crystal systemTetragonal
Crystal classDitetragonal dipyramidal (4/mmm)
H-M symbol: (4/m 2/m 2/m)
Space groupI41/amd
Unit cella = 6.21, c = 5.47 [Å] (approximated); Z = 4
Identification
Crystal habitpseudo-octahedral
Cleavage{110} and {010}, distinct
FractureSubconchoidal
Mohs scale hardness7-7.5
Density7.91 (calc.), 7.86 (meas.)
Optical propertiesUniaxial (+)
Refractive indexnω & nε >2
BirefringenceHigh
References[1][2]

Béhierite was named for Jean Béhier (1903–1965), who discovered the mineral in 1959, as a French mineralogist, active in the Service Géologique, on the island of Madagascar.[2]

Occurrence and association

Béhierite occurs in granitic pegmatites in Manjaka and Antsongombato, Madagascar. Associated minerals are albite, manganese-bearing apatite-group mineral, lepidolite, elbaite or elbaite–liddicoatite, feldspar, pollucite, quartz, rhodizite, and schiavinatoite.[1]

Crystal structure

Crystal structure of synthetic TaBO4 was refined by Range et al. (1996).[5] As béhierite is analogous to schiavinatoite, their crystal structures are expected to be similar.[6]

References
  1. "Béhierite (Ta,Nb)BO4 - Handbook of Mineralogy" (PDF). Handbookofmineralogy.org. Retrieved 2016-03-03.
  2. "Béhierite: Béhierite mineral information and data". Mindat.org. Retrieved 2016-03-03.
  3. Mrose, M.E., and Rose, H.J., 1961. Behierite, (Ta,Nb)BO4, a new mineral from Manjaka, Madagascar. Geological Society of America, Abstracts Annual Meetings 1961, 111A-111A
  4. "Holtite: Holtite mineral information and data". Mindat.org. Retrieved 2016-03-03.
  5. Range, K.J., Wildenauer, M., and Andratschke, M., 1996. Crystal structure of tantalum orthoborate, TaBO4. Zeitschrift für Kristallographie, 211-215
  6. Demartin, F., Diella, V., Gramaccioli, C.M., and Pezzotta, F., 2001. Schiavinatoite, (Nb,Ta)BO4, the Nb analogue of behierite. European Journal of Mineralogy 13, 159-165
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