Formula: NaFe3Al6(BO3)3Si6O21F
Reflected/transmitted colour: yellow
Pleochroism: w = yellow-brown, e = very pale yellow
Optical isotropy/anisotropy: uniaxial
Optical sign: -
Refractive indices: w = 1.735, e = 1.655
Birefringence δ: 0.08
2V angle:
Dispersion:
Optical orientation:
Optical axial plane:
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