Formula: NaFe(Si2O6)
Reflected/transmitted colour: pale to dark green and yellowish green
Pleochroism: α emerald green, deep green, β grass-green, deep green, γ brownish green, yellowish brown
Optical isotropy/anisotropy: biaxial
Optical sign: -
Refractive indices: α = 1. 750-1.776, β = 1.780-1.820, γ 1.795-1.836
Birefringence δ: 0.040-0.060
2Vα angle: 60-70°
Dispersion: r > v, moderate to strong
Optical orientation: α Λ z = 0-10° (in β obtuse), β = y, γ Λ x = 7-17°
Optical axial plane: (010)
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