Béhierite
| Béhierite | |
|---|---|
 Béhierite | |
| General | |
| Category | Borate |
| Formula (repeating unit) | (Ta,Nb)BO4 |
| 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 | [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
- ^ a b c "Béhierite (Ta,Nb)BO4 - Handbook of Mineralogy" (PDF). Handbookofmineralogy.org. Retrieved 2016-03-03.
- ^ a b c d "Béhierite: Béhierite mineral information and data". Mindat.org. Retrieved 2016-03-03.
- ^ 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
- ^ "Holtite: Holtite mineral information and data". Mindat.org. Retrieved 2016-03-03.
- ^ Range, K.J., Wildenauer, M., and Andratschke, M., 1996. Crystal structure of tantalum orthoborate, TaBO4. Zeitschrift für Kristallographie, 211-215
- ^ 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