Minium

Formula: Pb3O4

Reflected/transmitted colour: red to colourless, polished section pinkish yellow gray, influenced by strong internal reflections, normal colour is bluish

Pleochroism: strong, nearly colourless and deep reddish brown

Optical isotropy/anisotropy: uniaxial, polished section obscured by internal reflections

Optical sign:

Refractive indices: n = 2.422

Birefringence δ/bireflectance: weak with anomalous green interference colours, polished section weak, yellow gray or orange-gray to gray-bluish

2V angle:

Dispersion:

Optical orientation:

Optical axial plane:

 

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