Formula: Ba(Fe,Mn)2TiSi2O7(O,OH)2
Reflected/transmitted colour: yellow-brown
Pleochroism: a = yellow-red to reddish brown, b = yellow, g = pale yellow to greenish yellow
Optical isotropy/anisotropy: biaxial
Optical sign: -
Refractive indices: a = 1.805-1.808, b = 1.835, g = 1.860-1.862
Birefringence δ: 0.055
2V angle: 54-86°
Dispersion:
Optical orientation: b = b, a Ù a = 5.5°
Optical axial plane:
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