Formula: CaAl(Si,Al)4O8(OH)4.(H2O,Cl)
Reflected/transmitted colour: colourless
Pleochroism:
Optical isotropy/anisotropy: biaxial
Optical sign: +
Refractive indices: a = 1.533, b = 1.534, g = 1.538
Birefringence δ: 0.005
2V angle: 57-59°
Dispersion: r < v
Optical orientation: g = b, b Ù c = 10°
Optical axial plane:
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