Ahlfeldite

Formula: NiSeO3.2H2O

Reflected/transmitted colour: greenish to pink

Pleochroism: α pale green, β pale pink, γ pink

Optical isotropy/anisotropy: biaxial

Optical sign: -

Refractive indices: α = 1.709, β = 1.752, γ = 1.787

Birefringence δ: 0.078

2V angle: measured: 85° , calculated: 82°

Dispersion: r < v, strong

Optical orientation: β = b, γ ^ c = -16°

Optical axial plane:

 

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