Formula: (Ca,Na)2(Fe,Fe,Ti)6(Si,Be,Al)6O20
Reflected/transmitted colour:
Pleochroism:
Optical isotropy/anisotropy: Biaxial
Optical sign: -
Refractive indices: α = 1.78, γ = 1.82
Bireflectance/Birefringence δ: 0.04
2V angle:
Dispersion:
Optical orientation:
Optical axial plane:
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