Formula: Mg(Fe,Al)(BO3)O
Reflected/transmitted colour: RL pale gray with dark red internal reflections
Pleochroism: Brown (x), very dark brown or dark brownish red (z)
Optical isotropy/anisotropy: Biaxial, RL weak
Optical sign: ?
Refractive indices:
Bireflectance/Birefringence δ:
2V angle:
Dispersion:
Optical orientation:
Optical axial plane:
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