Formula: NaCr(Si2O6)
Reflected/transmitted colour: green or yellow
Pleochroism: α yellowish green, β grass green, γ emerald green
Optical isotropy/anisotropy: biaxial
Optical sign: -
Refractive indices: α = 1. 740-1.766, β = 1.756-1.778, γ 1.742-1.781
Birefringence δ: 0.015-0.022
2Vα angle: 53°
Dispersion: r > v, moderate to strong
Optical orientation: β = y, γ Λ z = 8-22°
Optical axial plane: (010)
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