Formula: Na(Mn,Mg,Fe)12Si12(O,OH)44
Reflected/transmitted colour:
Pleochroism: Nearly colourless or pale golden yellow (x), nearly colourless or yellowish brown (y), pale yellow or dark brown (z)
Optical isotropy/anisotropy: Biaxial
Optical sign: -
Refractive indices: α = 1.646-1.697, β = 1.664-1.72, γ = 1.676-1.732
Bireflectance/Birefringence δ: 0.030-0.035
2V angle: 70-76° (calculated), 70° (measured)
Dispersion:
Optical orientation:
Optical axial plane:
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