Vertumnite

Formula: Ca4Al4Si4O6(OH)24.3H2O

Reflected/transmitted colour:

Pleochroism:

Optical isotropy/anisotropy: Biaxial, rarely uniaxial (-)

Optical sign: -

Refractive indices: α = 1.531, β = 1.535, γ = 1.541

Bireflectance/Birefringence δ: 0.010

2V angle: 80° (calculated), 62° (measured)

Dispersion:

Optical orientation: X = c, Z Ù b = 16°

Optical axial plane:

 

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