Bornite

Formula: Cu₅FeS₄

Reflected/transmitted colour: opaque, polished section pinkish brown to orange, soon tarnishes purplish, violet or iridescent

Pleochroism: weak but noticeable

Optical isotropy/anisotropy: polished section usually weakly anisotropic, very fine-grained aggregates may appear isotropic

Optical sign:

Refractive indices:

Birefringence δ/bireflectance: polished section; often a slight bireflectance is perceptible on grain boundaries and on twin lamellae.

2V angle:

Dispersion:

Optical orientation:

Optical axial plane:

Light grayish grain of intimately intergrown isomertieite and arsenopalladinite (in the center of the picture), with pale yellow gold and brownish to violet bornite. Polished section (from microprobe analysis) in reflected light.

Origin: Noril'sk, Putoran Mts, Taymyrskiy Autonomous Okrug, Eastern-Siberian Region, Russia

Picture size: 0.1 mm

Owner: Thomas Witzke

 

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