Formula: TlAsS2
Reflected/transmitted colour: purple- to orange-red, polished section grayish white with a bluish tint with dark red internal reflections
Pleochroism: weak, β purple-red, γ orange-red
Optical isotropy/anisotropy: biaxial, polished section strong anisotropy, but obscured by internal reflections
Optical sign: + (?)
Refractive indices: n ≥ 2.72
Birefringence δ/bireflectance: polished section weak but noticeable
2V angle: large
Dispersion: r > v, strong
Optical orientation: α ,β ~ ┴ (100), γ = y
Optical axial plane:
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