Formula: (Mg,Al)8O2(SiO4)4(OH)2
Reflected/transmitted colour:
Pleochroism:
Optical isotropy/anisotropy: Biaxial
Optical sign: +
Refractive indices: α = 1.689-1.691, β = 1.691-1.693, γ = 1.712-1.715
Bireflectance/Birefringence δ: 0.023-0.024
2V angle: 34-36° (calculated), 25-30° (measured)
Dispersion:
Optical orientation:
Optical axial plane:
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