Formula: AsS
Reflected/transmitted colour: colourless to pale yellow, in polished section dull gray-white with abundant yellow to red internal reflections
Pleochroism: nearly colourless to pale golden yellow
Optical isotropy/anisotropy: biaxial, polished section strong anisotropy, but not perceptible in oil because of internal reflections
Optical sign: -
Refractive indices: α = 2.538, β = 2.684, γ = 2.704
Birefringence δ/bireflectance: ~ 0.174, polished section weak, but distinct, gray with reddish to gray with bluish tint
2V angle: 40-41°
Dispersion: r > v
Optical orientation: α Λ z = -11°
Optical axial plane:
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