Formula: (Na,K,Ca)2Al2Si7O18 . 7H2O
Reflected/transmitted colour: colourless
Pleochroism:
Optical isotropy/anisotropy: biaxial
Optical sign: -
Refractive indices: a = 1.4791, b = 1.4851, g = 1.4891
Birefringence δ: 0.01
2V angle: 78-79°
Dispersion:
Optical orientation: a = a, b = b, g = c
Optical axial plane:
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