Formula: Zn2(AsO4)(OH)
Reflected/transmitted colour: colourless, or faintly tinted
Pleochroism: in pale colours if cuprian or cobaltian
Optical isotropy/anisotropy: biaxial
Optical sign: +/-
Refractive indices: α = 1.708 - 1.722, β = 1.742 - 1.744, γ = 1.763 - 1.773
Birefringence δ: 0.055
2V angle: measured: 88° , calculated: 74° to 84°
Dispersion: r < v or r > v, strong
Optical orientation: α = a, β = c, γ = b
Optical axial plane:
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