Lalondeite

Formula(Na,Ca)6(Ca,Na)3Si16O38(F,OH)2·3H2O

Reflected/transmitted colour:

Pleochroism:

Optical isotropy/anisotropy: Biaxial

Optical sign: -

Refractive indices: α = 1.522, β = 1.528, γ = 1.529

Bireflectance/Birefringence δ: 0.007

2V angle: 44° (calculated), 48° (measured)

Dispersion:

Optical orientation:

Optical axial plane:

 

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