Vrbaite

Formula: Tl4Hg3Sb2As8S20

Reflected/transmitted colour: polished section grayish white with bluish tint with red internal reflections

Pleochroism:

Optical isotropy/anisotropy: biaxial, polished section distinct anisotropic, not as strong as for lorandite, blue or bluish green to reddish yellow

Optical sign: +

Refractive indices: n ≥ 2.72

Birefringence δ/bireflectance:

2V angle:

Dispersion: r > v

Optical orientation:

Optical axial plane:

 

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