Nacre-mimicking layered organic/inorganic hybrid materials exhibiting ultrahigh stiffness and strength frequently require multistep processing that is restricted to polar and even water-soluble polymers. Herein, nacre-mimetic hydrocarbon composites were fabricated by single-step injection molding. The key intermediates are organophilic ultrathin gamma-Al(OH)(3) (O-gibbsite) single-crystal nanoplatelets and all-hydrocarbon composites (All-PE) containing aligned, extended-chain ultrahigh-molecular-weight polyethylene (UHMWPE) as one-dimensional (1D) nanostructures embedded in a polyethylene (PE) matrix. This formation of flow-induced UHMWPE 1D nanostructures mimics chitin nanofibers in nacre and drives the alignment of O-gibbsite nanoplatelets to assemble bricks. Unprecedented high contents of up to 70 wt % O-gibbsite nanoplatelets are tolerated in injection molding. As verified by focused ion beam-scanning electron microscopy (FIB-SEM), the resulting brick-and-mortar architectures contain aligned O-gibbsite as bricks and UHMWPE/high-density polyethylene (HDPE) shish-kebab structures as mortar. The resulting nacre-mimetic hydrocarbon/O-gibbsite composites exhibit substantially improved mechanical properties, as evidenced by high tensile strength of 200 MPa and a superior notched Izod impact strength (28 kJ/m(2)). In contrast to other nacre-mimetic composites, these superb mechanical properties are retained after immersing the composites in water for several days. As gamma-Al(OH)(3) splits off the water at elevated temperature, nacre-inspired hydrocarbon composites are flame retardant despite the high flammability of hydrocarbons.