Formula: LiAl(Si2O6)
Reflected/transmitted colour: usually colourless
Pleochroism: kunzite α purple, γ colourless; hiddenite α green, γ colourless
Optical isotropy/anisotropy: biaxial
Optical sign: +
Refractive indices: α = 1. 648-1.662, β = 1.655-1.669, γ 1.662-1.679
Birefringence δ: 0.014-0.027
2Vγ angle: 58-68°
Dispersion: r < v
Optical orientation: α Λ x = 6-11°, β = y, γ Λ z = 20-26°
Optical axial plane: (010)
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