Formula: BaSO4
Reflected/transmitted colour: colourless
Pleochroism: slight in coloured varieties, absorption γ > β > α
Optical isotropy/anisotropy: biaxial
Optical sign: +
Refractive indices: α = 1.636-1.637, β = 1.637-1.639, γ = 1.647-1.649
Birefringence δ: ~ 0.012
2Vγ angle: 37°
Dispersion: r < v, weak
Optical orientation: α = z, β = y, γ = x
Optical axial plane: (010)
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