Formula: K2Na(Ca,Mn)2TiSi7O19(OH)
Reflected/transmitted colour:
Pleochroism: Colourless (X=Y), pale orange-brown (Z)
Optical isotropy/anisotropy: Biaxial
Optical sign: +
Refractive indices: α = 1.593-1.599, β = 1.621-1.627, γ = 1.666-1.673
Bireflectance/Birefringence δ: 0.073
2V angle: 68-78° (measured)
Dispersion: Strong
Optical orientation: X' ⋀ {010} = 1-4°, Y ⋀ {010} = 16-18°
Optical axial plane:
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