Formula: (Na,Ca)Al4(Si,Al)8O20(OH)4.2H2O
Reflected/transmitted colour:
Pleochroism:
Optical isotropy/anisotropy: Biaxial
Optical sign: -
Refractive indices: a=1.519, b=1.55, g=1.559
Bireflectance/Birefringence δ: 0.040
2V angle: 54 (calculated), 5-20 (measured)
Dispersion: r > v
Optical orientation:
Optical axial plane:
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