Formula: (Mg,Fe)2Al14B4Si4O37
Reflected/transmitted colour:
Pleochroism: Colourless (x), yellow (y), colourless (z)
Optical isotropy/anisotropy: Biaxial
Optical sign: -
Refractive indices: α = 1.614, β = 1.646, γ = 1.651
Bireflectance/Birefringence δ: 0.037
2V angle: 42° (calculated), 33-42° (measured)
Dispersion: Moderately strong, r > v
Optical orientation:
Optical axial plane:
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