Formula: Na(Sr,Ca)2Al5Si5O20·6H2O
Reflected/transmitted colour: Colourless
Pleochroism:
Optical isotropy/anisotropy: Biaxial
Optical sign: +
Refractive indices: α = 1.528, β = 1.532, γ = 1.540
Bireflectance/Birefringence δ: 0.012
2V angle: 72° (calculated), 62° (measured)
Dispersion: Weak, r > v
Optical orientation:
Optical axial plane:
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