Dufrénoysite

Formula: Pb2As2S5

Reflected/transmitted colour:  white, sometimes showing deep red internal reflections, dark red-brown in transmitted light

Pleochroism: very weak

Optical isotropy/anisotropy: strong, in brown-violet and dark green colours

Optical sign:

Refractive indices: n > 2.72

Bireflectance/Birefringence δ:

2V angle:

Dispersion:

Optical orientation:

Optical axial plane:

 

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