Belkovite

Formula: Ba3(Nb,Ti)6(Si2O7)2O12

Reflected/transmitted colour:

Pleochroism:

Optical isotropy/anisotropy: uniaxial

Optical sign: +

Refractive indices: w = 1.928, e = 2.002

Birefringence δ: 0.074

2V angle: 0-10° (anomalous)

Dispersion:

Optical orientation:

Optical axial plane:

 

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