Thenardite

Formula: Na2SO4

Reflected/transmitted colour: Colourless

Pleochroism: None

Optical isotropy/anisotropy: Biaxial

Optical sign: +

Refractive indices: α= 1.464–1.471, β = 1.473–1.477, γ = 1.481–1.485

Bireflectance/Birefringence δ: 0.013

2V angle: 86° (calculated), 83° (measured)

Dispersion: Weak, r > v

Optical orientation: X = c, Y = b, Z = a

Optical axial plane:

 

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