The utilization of slag from metallurgical processes supports resource conservation, which highlights the importance of understanding its properties. Characterization and analysis techniques are key to link chemical composition and phases to properties and process parameters. In this study the feasibility of transmission electron microscopy for phase analysis in nanoscale is tested. The same phases as in scanning electron microscopy investigations are observed, including copper droplets during their formation. Additionally phases with crystal structure are identified, which lattice spacings fit to spinel structures (Al, Mg, Fe) (Zn, Al, Cr, Fe)2O4 with spacegroup “F d¯ 3m ”. A high-resolution image of atom columns in industrial slag samples is provided, showing the possibility of transmission electron microscopy for analysis of crystalline phases in slag. © 2023, The Minerals, Metals & Materials Society and ASM International.