Rammelsbergite

Formula: NiAs2

Reflected/transmitted colour: opaque, polished section white, considerably whiter than other Ni-Co-Fe arsenides

Pleochroism:

Optical isotropy/anisotropy: polished section strong anisotropic, especially in oil, showing pinkish, brownish, greenish and blue colours (not as strong as for safflorite and löllingite)

Optical sign:

Refractive indices:

Birefringence δ/bireflectance: polished section in air very weak, weaker than for safflorite, in oil more distinct, yellowish white to bluish white

2V angle:

Dispersion:

Optical orientation:

Optical axial plane:

 

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