Formula: (Na,K)3Mg4(Al,Mg)6(Si,Al)24O60
Reflected/transmitted colour:
Pleochroism:
Optical isotropy/anisotropy: Uniaxial
Optical sign: +
Refractive indices: ω = 1.536, ε = 1.544
Bireflectance/Birefringence δ: 0.008
2V angle:
Dispersion:
Optical orientation:
Optical axial plane:
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