Formula: Cu7(Tl,Ag)Se4
Reflected/transmitted colour: gray-white to pinkish cream and brown, colour is different for each locality, depending on chemical composition
Pleochroism:
Optical isotropy/anisotropy: weak but distinct anisotropic, in brownish tones, extinction // cleavage
Optical sign:
Refractive indices:
Bireflectance/Birefringence δ: weak in air, distinct in oil
2V angle:
Dispersion:
Optical orientation:
Optical axial plane:
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