Formula: Na5Nb3Ti(Si2O7)3O2F2.2Na3PO4
Reflected/transmitted colour:
Pleochroism:
Optical isotropy/anisotropy: Biaxial
Optical sign: +
Refractive indices: α = 1.636-1.639, β = 1.651-1.656, γ = 1.68-1.683
Bireflectance/Birefringence δ: 0.044
2V angle: 86° (calculated), 53-86° (measured)
Dispersion:
Optical orientation:
Optical axial plane:
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