Andremeyerite

Formula: BaFe2Si2O7

Reflected/transmitted colour: pale green

Pleochroism: a = pale bluish green, b = g = colourless with faint brownish tint

Optical isotropy/anisotropy: biaxial

Optical sign: +

Refractive indices: a = 1.740, b = 1.740, g = 1.760

Birefringence δ: 0.02

2V angle: 0-80°

Dispersion: very strong

Optical orientation: g = b, a Ù c = 2° at 670 nm to 61° at 470 nm

Optical axial plane:

 

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