Abstract: The chemistry and crystallography of type georgiadesite from Laurion, Greece, have been reexamined using electron microprobe analysis along with powder and single-crystal X-ray diffraction. Georgiadesite is monoclinic, P2₁/c, with a = 13.803(10), b = 7.910(2), c = 10.812(4) Å, and β = 102.68(3)°. No twinning was observed. The probable chemical formula is either Pb₁₆(AsO₄)₄Cl₁₄O₂(OH)₂ or Pb₁₆(AsO₄)₄Cl₁₄(OH)₆. The calculated densities for these formulae are 6.39 and 6.44 g/cm³, respectively, compared to a measured value of 6.3 + 0.3 g/cm³.