Formula: (Fe,Mg)9Al4Cl18(OH)12.14H2O
Reflected/transmitted colour:
Pleochroism:
Optical isotropy/anisotropy: Uniaxial
Optical sign: +
Refractive indices: ω = 1.522, ε = 1.552
Bireflectance/Birefringence δ: 0.030
2V angle:
Dispersion:
Optical orientation:
Optical axial plane:
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