Formula: FeAl2(PO4)2(OH)2.6H2O
Reflected/transmitted colour:
Pleochroism: Colourless (x), blue (y), colourless (z)
Optical isotropy/anisotropy: Biaxial
Optical sign: +
Refractive indices: α = 1.551, β = 1.555, γ = 1.562
Bireflectance/Birefringence δ: 0.011
2V angle: 76° (calculated), 32° (measured)
Dispersion: Marked, r > v
Optical orientation: Z ≈ ^ {010}
Optical axial plane:
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