Formula: Na4K3(Fe,Mn,Ti)2Si8O20(OH)4 . 4H2O
Reflected/transmitted colour:
Pleochroism: Light green or yellowish green (x and y), dark olive green (z)
Optical isotropy/anisotropy: Biaxial
Optical sign: +
Refractive indices: α = 1.569, β = 1.574, γ = 1.590
Bireflectance/Birefringence δ: 0.021
2V angle: 60° (calculated), 58° (measured)
Dispersion: Medium, r > v
Optical orientation:
Optical axial plane:
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