Tilleyite

Formula: Ca3(Si2O7).2CaCO3

Reflected/transmitted colour: colourless

Pleochroism: -

Optical isotropy/anisotropy: biaxial

Optical sign: +

Refractive indices: α = 1.605-1.617, β = 1.626-1.635, γ = 1.651-1.654

Birefringence δ: 0.035-0.046

2Vγ angle: 85-89°

Dispersion: r < v

Optical orientation: α Λ z = 24°, β = y, γ Λ{20-1} cleavage plane = ~12°

Optical axial plane:

 

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