Formula: (Fe,Mn)2(PO4)(OH)
Reflected/transmitted colour:
Pleochroism:
Optical isotropy/anisotropy: Biaxial
Optical sign: +
Refractive indices: α = 1.741, β = 1.742, γ = 1.790
Bireflectance/Birefringence δ: 0.049
2V angle: 51° (measured)
Dispersion: Strong, r > v
Optical orientation:
Optical axial plane:
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