Formula: AlFe4(SO4)6(OH,O)2.20H2O
Reflected/transmitted colour: colourless to yellow
Pleochroism: β colourless, γ greenish yellow
Optical isotropy/anisotropy: biaxial
Optical sign: +
Refractive indices: α = 1.529, β = 1.535, γ = 1.585
Birefringence δ: 0.056
2V angle: measured: 45°, calculated: 40°
Dispersion:
Optical orientation:
Optical axial plane:
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