Formula: Na(Li,Al)3Al6B3Si6(O,OH)30(OH,F)
Reflected/transmitted colour: colourless
Pleochroism: variable in intensity, normally very strong, absorption always w > ε
Optical isotropy/anisotropy: uniaxial
Optical sign: -
Refractive indices: ε = 1.615-1.630, w = 1.633-1.651
Birefringence δ: 0.017-0.021
2V angle:
Dispersion: weak
Optical orientation:
Optical axial plane:
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