Delhayelite

Formula: (Na,K)10Ca5Al6Si32O80(Cl2,F2,SO4)3 . 18H2O

Reflected/transmitted colour:

Pleochroism:

Optical isotropy/anisotropy: Biaxial

Optical sign: -

Refractive indices: α = 1.532, β = 1.532, γ = 1.532

Bireflectance/Birefringence δ: 0.000

2V angle: 0° (calculated), 83° (measured)

Dispersion:

Optical orientation:

Optical axial plane:

 

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