Béhierite
| Béhierite | |
|---|---|
| General | |
| Category | Borate |
| Formula (repeating unit) |
(Ta,Nb)BO4 |
| Crystal symmetry | Tetragonal (point group 4/mmm); Space group: I41/amd |
| Unit cell | a=6.21, c=5.47 [Å] (approximated) |
| Identification | |
| Crystal habit | pseudo-octahedral |
| Crystal system | Monoclinic |
| 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
- ↑ 1.0 1.1 1.2 Lua error in package.lua at line 80: module 'strict' not found.
- ↑ 2.0 2.1 2.2 2.3 Lua error in package.lua at line 80: module 'strict' not found.
- ↑ 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
- ↑ Lua error in package.lua at line 80: module 'strict' not found.
- ↑ 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
