Covellite

Formula: CuS

Reflected/transmitted colour: opaque, polished section: basal section indigo blue, cross section show extreme high bireflectance both in air and oil

Pleochroism:

Optical isotropy/anisotropy: uniaxial; polished section extremely strong anisotropy; 45° fiery orange, reddish brown

Optical sign: +

Refractive indices: w = 1.45, ε = 2.62

Birefringence δ/bireflectance: ~ 1.17, polished section extraordinary high, most characteristic feature, in air w deep blue with violet tint, ε bluish white, in oil O purple to violet-red, scratches may appear as orange-red ligth lines

2V angle:

Dispersion: strong

Optical orientation: ε//z, w z

Optical axial plane:

 

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