Formula: NaAl(Si2O6)
Reflected/transmitted colour: colourless
Pleochroism: -
Optical isotropy/anisotropy: biaxial
Optical sign: +
Refractive indices: α = 1. 640-1.681, β = 1.645-1.684, γ 1.652-1.692
Birefringence δ: 0.006-0.021
2Vγ angle: 60-96°
Dispersion: r > v, moderate to strong
Optical orientation: α Λ x = 16-23°, β = y, γ Λ z = 32-55°
Optical axial plane: (010)
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