Formula: (CaxNa1-x)(Si3-xAl1+x)4O8 (x= 0.7 - 0.9)
Reflected/transmitted colour: Colourless
Pleochroism:
Optical isotropy/anisotropy: Biaxial
Optical sign: -
Refractive indices: α = 1.563-1.572, β = 1.568-1.5784, γ = 1.573-1.583
Bireflectance/Birefringence δ: 0.010-0.011
2V angle: 80-88° (calculated), 87° to -78° (low); 81° to -83° (high) (measured)
Dispersion: Weak, r < v
Optical orientation:
Optical axial plane:
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