Formula: Fe8-2x[(As1-xSx)O4]6.5H2O
Reflected/transmitted colour:
Pleochroism: Lemon yellow (X=Z), orange (Y)
Optical isotropy/anisotropy: Biaxial
Optical sign: -
Refractive indices: α = 1.94, β = 2.04, γ = 2.05
Bireflectance/Birefringence δ: 0.11
2V angle: 32° (calculated), 2-5° (measured)
Dispersion: Slight, r > v
Optical orientation: X = a, Y = c, Z = b
Optical axial plane:
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