Formula: NaCaAl3Si17O40.>7H2O
Reflected/transmitted colour:
Pleochroism:
Optical isotropy/anisotropy: Biaxial
Optical sign: +
Refractive indices: α = 1.476, β = 1.478, γ = 1.483
Bireflectance/Birefringence δ: 0.007
2V angle:
Dispersion: Moderate, r < v
Optical orientation:
Optical axial plane:
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