Formula: Na3(Mg,Fe)4(Al,Fe)(Si8O22)(OH,F)2
Reflected/transmitted colour: pale bluish green
Pleochroism: α bluish green, β light bluish green, γ pale yellowish green, absorption α > β > γ
Optical isotropy/anisotropy: biaxial
Optical sign: -
Refractive indices: α = 1.612-1.640, β = 1.625-1.646, γ = 1.630-1.655
Birefringence δ: 0.013-0.020
2Vα angle: 72-80°
Dispersion: r > v, strong
Optical orientation: β = y, γ Λ z = 18-53°
Optical axial plane: (010)
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