Formula: Na2Al4(Si6Al2O20)(OH)4
Reflected/transmitted colour: colourless
Pleochroism: -
Optical isotropy/anisotropy: biaxial
Optical sign: -
Refractive indices: α = 1.654-1.580, β = 1.594-1.609, γ = 1.600-1.609
Birefringence δ: 0.028-0.038
2Vα angle: 0-40°
Dispersion: r > v
Optical orientation: α Λ z = ~5°, β = ~ x, γ = y
Optical axial plane: ┴ (010)
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