Petalite

Formula: LiAlSi4O10

Reflected/transmitted colour: colourless

Pleochroism: -

Optical isotropy/anisotropy: biaxial

Optical sign: +

Refractive indices: α = 1.504-1.507, β = 1.510-1.513, γ = 1.516-1.523

Birefringence δ: 0.011-0.017

2Vγ angle: 82-84°

Dispersion: r > v

Optical orientation: α Λ x = 2-8°, β Λ z = 24-30°, γ = y

Optical axial plane: (010)

 

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