Formula: (Ba,K,Na)3Ti2Si4O14
Reflected/transmitted colour: brownish
Pleochroism: a = colourless, b = yellowish brown, g = reddish brown
Optical isotropy/anisotropy: biaxial
Optical sign: +
Refractive indices: a = 1.730, b = 1.735, g = 1. 791
Birefringence δ: 0.06
2V angle: 7°
Dispersion: r < v, strong
Optical orientation: a = a, b = b, g = c
Optical axial plane:
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