Formula: Ca5(PO4)3(OH,F,Cl)
Reflected/transmitted colour: generally colourless
Pleochroism: coloured varieties may show weak to moderate pleochroism, with absorption ε > w
Optical isotropy/anisotropy: uniaxial
Optical sign: -
Refractive indices: ε = 1.624-1.666, w = 1.629-1.667
Birefringence δ: 0.001-0.007
2V angle:
Dispersion: moderate
Optical orientation:
Optical axial plane:
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