Formula: (Fe,Mg)3Si4O10(OH)2
Reflected/transmitted colour:
Pleochroism:
Optical isotropy/anisotropy: Biaxial
Optical sign: -
Refractive indices: α = 1.578-1.583, β = 1.578-1.622, γ = 1.615-1.623
Bireflectance/Birefringence δ: 0.037-0.040
2V angle: 0-16° (calculated), 4° (measured)
Dispersion:
Optical orientation:
Optical axial plane:
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