Formula: PbZn(VO4)(OH)
Reflected/transmitted colour: yellow to greenish and brownish yellow, polished section gray to grayish blue. Internal reflections are rare, colourless to brownish.
Pleochroism: weak to strong, α = β canary-yellow to greenish yellow, γ brownish yellow
Optical isotropy/anisotropy: biaxial, polished section very strong anisotropic
Optical sign: -, rarely +
Refractive indices: α = 2.185, β = 2.265, γ = 2.35
Birefringence δ/bireflectance: ~ 0.12, polished section strong in air and in oil, gray to grayish blue
2V angle: ~ 90°
Dispersion: r > v, rarely r < v
Optical orientation: α = z, β = y, γ = x
Optical axial plane:
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