Formula: NiAs
Reflected/transmitted colour: opaque, polished section yellowish or light pink to brownish pink
Pleochroism: high
Optical isotropy/anisotropy: polished section very strong anisotropic, yellowish, grayish green, violet-blue, bluish gray. Straight but no complete extinction. Basal sections appear isotropic
Optical sign:
Refractive indices:
Birefringence δ/bireflectance: polished section strong and typical bireflectance, w yellowish pink or light pink, ε brownish pink
2V angle:
Dispersion:
Optical orientation:
Optical axial plane:
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