The new mineral pendevilleite-(Y) (IMA 2022-054), ideally Mg2Y3Al(UO2)2(CO3)7(OH)6(H2O)16, was found in the famous Kamoto-East open-cut, Lualaba province, Democratic Republic of Congo and named after Jean-Marie Pendeville (1936–2002), a specialist in collecting minerals of Congo. The new mineral occurs as extremely thin blades (up to ∼0.08–0.10 mm in length and only ∼1 μm thick), often forming lichen-like aggregates and crusts. It is associated with kamotoite-(Y), astrocyanite-(Ce) and shabaite-(Nd), uranophane and sklodowskite. Pendevilleite-(Y) crystals are whitish or greyish-white, locally pale-bluish white. The mineral is brittle; has an irregular fracture and a Mohs hardness of ∼2. Cleavage is perfect on {001}. Electron microprobe analyses provided (on the basis of 2 apfu U with CO32–, H2O derived from the structure and OH– to keep the electroneutrality) formula Mg1.78[(Y1.42Gd0.36Dy0.33Nd0.16Er0.14Sm0.13Eu0.12Tb0.05Ho0.04Yb0.04Ce0.03Tm0.03Pr0.01)Σ2.86 Ca0.11Pb0.01]Σ2.98Al0.88(UO2)2(CO3)7(OH)5.02(H2O)16. Pendevilleite-(Y) is triclinic, P$\overline 1 $, a = 11.9130(3) Å, b = 13.5252(11) Å, c = 16.1531(3) Å, α = 107.052(3)°, β = 92.7765(19)°, γ = 109.676(4)° and V = 2311.5(2) Å3 (Z = 2) at 97 K. The crystal structure (dynamical refinement against 3D ED data; R1 = 0.0948 for 1168 [I > 3σ(I)] reflections) possesses a large heteropolyhedral framework based on both a finite [(UO2)(CO3)3]4– cluster (UTC cluster) and a dimeric [(UO2)2(CO3)4(OH)2]6– unit formed due to olation of uranyl polyhedra. There are three M sites in the structure, occupied by Y3+ and Ln3+, with symmetry-related equivalents forming a polyoxometalate cluster of the general composition [(Y,Ln)6(OH)8(H2O)4(CO3)4]2+. Additionally, there is one Al site in the structure (symmetrically related equivalents forming a dimer of composition [Al2O2(OH)8]6–), and two Mg sites in octahedral coordination MgO2(H2O)4. In the sizeable channels of the framework (running parallel to c), there are at least eight independent partially occupied and disordered O sites of the H2O molecules.