Welshite

Formula: Ca2SbMg4FeSi4Be2O20

Reflected/transmitted colour:

Pleochroism:

Optical isotropy/anisotropy: Biaxial

Optical sign: +

Refractive indices: α = 1.81, β = 1.83

Bireflectance/Birefringence δ: > 0.02

2V angle: 45° (measured)

Dispersion:

Optical orientation:

Optical axial plane:

 

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