Formula: (Mn,Mg)5Si8O20(OH)2.8-9H2O
Reflected/transmitted colour:
Pleochroism: Distinct
Optical isotropy/anisotropy: Biaxial
Optical sign: ?
Refractive indices: α = 1.53, γ = 1.559
Bireflectance/Birefringence δ: 0.029
2V angle:
Dispersion:
Optical orientation:
Optical axial plane:
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