Formula: Na3(Na,K)Al4Si4O16
Reflected/transmitted colour: colourless
Pleochroism: -
Optical isotropy/anisotropy: uniaxial
Optical sign: -
Refractive indices: ε = 1.526-1.542, w = 1.529-1.546
Birefringence δ: 0.003-0.005
2V angle:
Dispersion: weak
Optical orientation:
Optical axial plane:
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