Formula: Al2SiO5
Reflected/transmitted colour: normally colourless, may be pinkish or greenish
Pleochroism: in coloured varieties weak, α rose-pink, β and γ greenish yellow
Optical isotropy/anisotropy: biaxial
Optical sign: -
Refractive indices: α = 1.633-1.642 (viridine has higher values), β = 1.639-1.644, γ = 1.644-1.650
Birefringence δ: 0.009-0.12
2Vα angle: 73-86°
Dispersion: r < v
Optical orientation: α = z, β = y, γ = x
Optical axial plane: (010)
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