Formula: (K,Na,Ba)(Al,Si)4O8
Reflected/transmitted colour: colourless
Pleochroism: -
Optical isotropy/anisotropy: biaxial
Optical sign: + or -
Refractive indices: α = 1.520-1.542, β = 1.524-1.545, γ = 1.526-1.547
Birefringence δ: 0.005-0.010
2Vγ angle: 101-132°
Dispersion: r > v
Optical orientation: α Λ x = 0-20°, γ = y
Optical axial plane: ┴ (010)
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