Formula: Mg6(Si8O20)(OH)4
Reflected/transmitted colour: colourless
Pleochroism: -
Optical isotropy/anisotropy: biaxial
Optical sign: -
Refractive indices: α = 1.539-1.550, β = 1.589-1.594, γ = 1.589-1.600
Birefringence δ: ~ 0.05
2Vα angle: 0-30°
Dispersion: r > v
Optical orientation: α Λ z = ~ 10°, β ~ x, γ = y
Optical axial plane: ┴ (010)
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