Formula: CaAlSiO4(OH)
Reflected/transmitted colour: Colourless
Pleochroism: Colourless or yellowish brown (X), colourless (Y=Z)
Optical isotropy/anisotropy: Biaxial
Optical sign: -
Refractive indices: α = 1.700, β = 1.725, γ = 1.730
Bireflectance/Birefringence δ: 0.030
2V angle: 46° (calculated), 44-48° (measured)
Dispersion: Strong to very strong, r < v
Optical orientation: X = c, Y = b, Z = a
Optical axial plane:
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