Formula: (Ca,Na)(Mg,Fe)3Al5Mg(BO3)Si6O18(OH,F)4
Reflected/transmitted colour:
Pleochroism: Light brown to colourless (E), brown to pale yellow(O)
Optical isotropy/anisotropy: Uniaxial
Optical sign: -
Refractive indices: ε = 1.619-1.639, ω = 1.637-1.668
Bireflectance/Birefringence δ: 0.018-0.029
2V angle:
Dispersion:
Optical orientation:
Optical axial plane:
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