Formula: Mn4AsSi3O12(OH)
Reflected/transmitted colour:
Pleochroism:
Optical isotropy/anisotropy: Biaxial
Optical sign: +
Refractive indices: α = 1.745, β = 1.751, γ = 1.760
Bireflectance/Birefringence δ: 0.015
2V angle: 80° (calculated), 38-46° (measured)
Dispersion: Inclined
Optical orientation: X @ a, Y = b, Z @ c
Optical axial plane:
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