Formula: Na,Ca)(Fe,Fe,Mg,Al)Si2O6
Reflected/transmitted colour:
Pleochroism:
Optical isotropy/anisotropy: biaxial
Optical sign: -
Refractive indices: α = 1.700 - 1.760, β = 1.710 - 1.800, γ = 1.730 - 1.813
Birefringence δ: 0.030 - 0.053
2V angle: measured: 70° to 110°, calculated: 58° to 72°
Dispersion:
Optical orientation:
Optical axial plane:
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