Béhierite

Béhierite
General
Category Borate
Formula
(repeating unit)		 (Ta,Nb)BO4
Crystal system Monoclinic
Unit cell a=6.21, c=5.47 [Å] (approximated)
Identification
Crystal habit pseudo-octahedral
Crystal symmetry

Tetragonal (point group 4/mmm);

Space group: I41/amd
Cleavage {110} and {010}, distinct
Fracture Subconchoidal
Mohs scale hardness 7-7.5
Density 7.91 (calc.), 7.86 (meas.)
Optical properties Uniaxial (+)
Refractive index nω & nε >2
Birefringence High
References [1][2]

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 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. 1 2 3 "Béhierite (Ta,Nb)BO4 - Handbook of Mineralogy" (PDF). Handbookofmineralogy.org. Retrieved 2016-03-03.
  2. 1 2 3 4 "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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