Béhierite is a very rare mineral,[2] the tantalum endmember of a borate solid solution series with formula (Ta,Nb)BO4.[4][3] The niobium analogue is schiavinatoite.
Béhierite | |
---|---|
General | |
Category | Borate |
Formula (repeating unit) | (Ta,Nb)BO4 |
IMA symbol | Béh[1] |
Strunz classification | 6.AC.15 |
Crystal system | Tetragonal |
Crystal class | Ditetragonal dipyramidal (4/mmm) H-M symbol: (4/m 2/m 2/m) |
Space group | I41/amd |
Unit cell | a = 6.21, c = 5.47 [Å] (approximated); Z = 4 |
Identification | |
Crystal habit | pseudo-octahedral |
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 | [2][3] |
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. Both have zircon-type structure (tetragonal, space group I41/amd) and are found in pegmatites.[3] Béhierite and holtite are minerals with essential tantalum and boron.[5]
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.[3]
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.[2]
Crystal structure
Crystal structure of synthetic TaBO4 was refined by Range et al. (1996).[6] As béhierite is analogous to schiavinatoite, their crystal structures are expected to be similar.[7]
References
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