Abstract: The crystal structure of botallackite, Cu₂(OH)₃Cl, monoclinic, a = 5.717(1), b = 6.126(1), c = 5.636(1)Å, β = 93.07(1)°, V = 197.06(5)ų, space group P2₁/m, Z = 1, has been refined to an R index of 3.8% for 350 observed (4σ) reflections, measured with Mo-Kα X-radiation on an automatic four-circle diffractometer. The structure consists of sheets of edge-sharing Cuϕ₆ (ϕ = unspecified anion) octahedra of composition Cu₂(OH)₃Cl; these sheets are // {100}, and are joined by hydrogen bonding between oxygen and chlorine anions, thus accounting for the perfect {100} cleavage and the platy habit of botallackite.