Formula: (Ca,Na)(Mg,Fe,Al)(Si2O6)
Reflected/transmitted colour: colourless to pale green
Pleochroism: feeble, α colourless, β very pale green, γ very pale green, blue green (darker in ferroan variety)
Optical isotropy/anisotropy: biaxial
Optical sign: +
Refractive indices: α = 1. 662-1.701, β = 1.670-1.712, γ 1.685-1.723
Birefringence δ: 0.012-0.028
2Vγ angle: 56-84°
Dispersion: r > v, moderate
Optical orientation: β = y, γ Λ z = 34-48°
Optical axial plane: (010)
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