Banalsite

Formula: BaNa2Al4Si4O16

Reflected/transmitted colour: colourless

Pleochroism:

Optical isotropy/anisotropy: biaxial

Optical sign: +

Refractive indices: a = 1.5695, b = 1.5710, g = 1.5775

Birefringence δ: 0.08

2V angle: 52° (calculated), 41° (measured)

Dispersion:

Optical orientation: a = c, b = a, g = b

Optical axial plane:

 

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