Formula: [](CaNa)(Mg,Fe)4(Al,Fe)(SI,Al)8O22(OH)2
Reflected/transmitted colour: Colourless to pale blue
Pleochroism: Colourless (x), light blue-violet (y), light blue (z)
Optical isotropy/anisotropy: Biaxial
Optical sign: +
Refractive indices: α = 1.636, β = 1.646, γ = 1.658
Bireflectance/Birefringence δ: 0.022
2V angle: 64° (measured)
Dispersion: Strong, r > v
Optical orientation: Z Ù c = 16°
Optical axial plane:
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