Formula: Ca2Al2O.(Al,Fe)OH(Si2O7)(SiO4)
Reflected/transmitted colour: yellow-green
Pleochroism: α colourless, pale yellow, pale green, β greenish yellow, γ yellowish green
Optical isotropy/anisotropy: biaxial
Optical sign: -
Refractive indices: α = 1.715-1.751, β = 1.725-1.784, γ = 1.734-1.797
Birefringence δ: 0.015-0.051
2V angle: 90-116°
Dispersion: r > v (over α)
Optical orientation: α Λ z = 0-15°, β = y
Optical axial plane: (010)
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