Formula: Ca2(Al,Fe)(AlSi3O10)(OH)2
Reflected/transmitted colour: colourless
Pleochroism: -
Optical isotropy/anisotropy: biaxial
Optical sign: +
Refractive indices: α = 1.612-1.640, β = 1.621-1.650, γ = 1.639-1.670
Birefringence δ: 0.022-0.035
2Vγ angle: 64-71°
Dispersion: usually r < v
Optical orientation: α = x, β = y, γ = z
Optical axial plane: (010)
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