Formula: (K,Na,Ca)3(Mn,Fe)7(Zr,Nb)2Si8O27(OH,F)4
Reflected/transmitted colour:
Pleochroism: Dark yellow (x), dark yellow (y), brown (z)
Optical isotropy/anisotropy: Biaxial
Optical sign: -
Refractive indices: α = 1.708, β = 1.738, γ = 1.747
Bireflectance/Birefringence δ: 0.039
2V angle: 56° (calculated), 62° (measured)
Dispersion:
Optical orientation:
Optical axial plane:
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