Formula: Na2AlSi3O8(OH)
Reflected/transmitted colour: Colourless
Pleochroism:
Optical isotropy/anisotropy: Biaxial
Optical sign: +
Refractive indices: α = 1.504, β = 1.508-1.509, γ = 1.543-1.545
Bireflectance/Birefringence δ: 0.039-0.041
2V angle: 40-42° (calculated), 32-39° (measured)
Dispersion:
Optical orientation:
Optical axial plane:
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