Formula: NaNa2(Mg,Fe)2Si8O22(OH)2
Reflected/transmitted colour:
Pleochroism:
Optical isotropy/anisotropy: Biaxial
Optical sign: -
Refractive indices: α = 1.660, β = 1.662, γ = 1.664
Bireflectance/Birefringence δ: 0.004
2V angle: 88° (calculated), 33-40° (measured)
Dispersion:
Optical orientation:
Optical axial plane:
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