Formula: Mg(OH,F)2.Mg2(SiO4)
Reflected/transmitted colour: pale yellow to colourless
Pleochroism: α pale yellow, β very pale yellow, γ colourless
Optical isotropy/anisotropy: biaxial
Optical sign: +
Refractive indices: α = 1.563-1.567, β = 1.567-1.579, γ = 1.590-1.593
Birefringence δ: 0.026-0.027
2Vγ angle: 44-50°
Dispersion: r > v
Optical orientation: α = x, β = z, γ = y
Optical axial plane: (001)
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