Bournonite

FormulaPbCuSbS3

Reflected/transmitted colour: opaque, polished section grayish white with a distinct blue or bluish green tint

Pleochroism: polished section very weak

Optical isotropy/anisotropy: polished section weak anisotropy in air, distinct in oil (especially when twinned), pale blue, greenish gray, brownish yellow, dark brown, purplish

Optical sign:

Refractive indices:

Birefringence δ/bireflectance: polished section; in air weak, only visible on grain boundaries and on twin lamellae, in oil distinct, white with a bluish green tint to white with an olive-green tint

2V angle:

Dispersion:

Optical orientation:

Optical axial plane:

 

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