Belloite, a new copper hydroxide chloride, ideally Cu(OH)Cl, is monoclinic, space group P21/a, with a = 5.552(3) Å, b = 6.668(2) Å, c = 6.124(2), β = 115.00° (3) Å, cell volume 205.47 Å3, Z = 4, from powder diffraction data. The strongest reflections in the X-ray powder diffraction data are (dmeas., I, hkl) 5.553 (100) (001), 2.758 (52) (112̄) (121̄), 2.516 (18) (200), 2.241 (27) (122̄), 1.851 (21) (213̄) (003). The mineral occurs on material from an abandoned mine near Sierra Gorda, northeast of Antofagasta, Chile. It forms aggregates of yellowish green to olive green micro-crystals closely associated with nitratine and paratacamite. Electron microprobe and CHN analyses give CuO 68.84, Cl 26.35 and H2O 7.47 wt.%, leading to an empirical formular of Cu1.05(OH)1.00O0.10Cl0.90, simplified Cu(OH)Cl. Belloite is identical with the synthetic Cu(OH)Cl of ICDD-PDF 23-1063, of which the structure has been determined by EFFENBERGER (1984).