Formula: As2S3
Reflected/transmitted colour: yellow to greenish yellow, polished section
Pleochroism: β = yellow, γ = greenish yellow, polished section strong, white to gray white with reddish tint
Optical isotropy/anisotropy: biaxial, polished section strong but barely observable due to strong internal reflections (especially in oil)
Optical sign: -
Refractive indices: α = 2.40, β = 2.81, γ = 3.02
Birefringence δ/bireflectance: 0.62, polished section strong in air, //α white, //β dull gray with reddish tint, //γ dull gray-white
2V angle: -76°
Dispersion: r > v, strong
Optical orientation: α = y, γ Λ z = 2°
Optical axial plane:
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