Béhierite

Béhierite is a very rare borate mineral,^[2] and the tantalum endmember of a (Nb,Ta)BO₄ solid solution series formed with schiavinatoite, its niobium analogue.^[4][3]

Béhierite
General
Category	Borate
Formula	TaBO4
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]