Formula: α-Al2O3
Reflected/transmitted colour: weakly coloured (gray, red, blue, green, yellow) to colourless
Pleochroism: absorption w > ε, e.g. in thick samples w dark blue, ε light blue or w blue and e yellow-green
Optical isotropy/anisotropy: uniaxial
Optical sign: -
Refractive indices: ε = 1.760-1.764, w = 1.768-1.772
Birefringence δ: 0.008-0.009
2V angle:
Dispersion: moderate
Optical orientation:
Optical axial plane:
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