Abstract: Obradovicite, ideal formula H₄CuFe₂(AsO₄) (MoO₄)₅ · 12H₂O, occurs as fine pea-green clusters on quartz from Chuquicamata, Chile. Obradovicite is orthorhombic, space group Pcnm; a = 15.046, b = 14.848, c = 11.056 Å, Z = 4. The strongest powder pattern lines are (d Å, I, hkl) 10.565(8)(110), 8.906(10)(101), 7.424(8)(020), 5.733(5)(211), 3.761(3)(400), 3.686(4)(032), 3.466(3)(411), 3.344(4)(420). It is biaxial positive with α = 1.790, β = 1.798, γ = 1.811, 2V_z = 81°, a = Z, b = X, c = Y, with strong dispersion and pale yellow pleochroism. Specific gravity is 3.55 (meas.) or 3.68 (calc.) and the Mohs hardness is 2½ with no obvious cleavage. Obradovicite is similar to betpakdalite and sodium-betpakdalite except that it contains essential Cu and K (K > Na).