Formula: NaMnSi2O6
Reflected/transmitted colour:
Pleochroism: Strong, lemon-yellow to pale yellow (X), raspberry red to brownish red (Y), blood-red to reddish purple (Z)
Optical isotropy/anisotropy: Biaxial
Optical sign: -
Refractive indices: α = 1.734-1.750, β = 1.769-1.850, γ = 1.835-1.870
Bireflectance/Birefringence δ: 0.091
2V angle: 64° (calculated), 15-85° (measured)
Dispersion: Very weak
Optical orientation: Y = b, X Ù c = 19-25°
Optical axial plane:
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