Bendadaite, ideally Fe²⁺Fe³⁺2(AsO₄)2(OH)2*4H₂O, is a new member of the arthurite group. It was found as a weathering product of arsenopyrite on a single hand specimen from the phosphate pegmatite Bendada, central Portugal (type locality). Cotype locality is the granite pegmatite of Lavra do Almerindo (Almerindo quarry), Linopolis, Divino das Laranjeiras county, Minas Gerais, Brazil. Further localities are the Veta Negra mine, Copiapo province, Chile, Oumlil, Bou Azzer district, Morocco, and Pira Inferida yard, Fenugu Sibiri mine, Gonnosfanadiga, Medio Campidano Province, Sardinia, Italy. Type bendadaite occurs as blackish green to dark brownish tufts (< 0.1 mm in length) and flattened radiating aggregates, in intimate association with an intermediate member of the scorodite-mansfieldite series. It is monoclinic, space group P₂₁/c, with a = 10.239(3) Å, b = 9.713(2) Å, c = 5.552(2) Å, β = 94.11(2)^o, V = 550.7(2) ų, Z = 2. The empirical formula is (Fe²⁺_0.52Fe³⁺_0.32__0.16)_∑1.00(Fe³⁺_1.89Al_0.11)_∑2.00(As_1.87P_0.13)_∑2.00O₈(OH)_2.00*4H₂O, based on 2(As,P) and assuming ideal 8O, 2(OH), 4H₂O and complete occupancy of the ferric iron site by Fe³⁺ and Al. The crystal structure of bendadaite was solved using a crystal from the cotype locality with the composition (Fe²⁺0.95?0.05)?1.00(Fe³⁺1.80Al_0.20)_∑2.00(As_1.48P_0.52)_∑2.00O₈(OH)₂₂O, and confirms an arthurite-type atomic arrangement.