Minerals have complex crystal structures, but many common minerals are built from the same chemical building blocks. TotBlocks is a novel, open-source tool for investigating these structures. It consists of 3D-printed modules representing the silica tetrahedra and metal–oxygen octahedra that form the shared chemical building blocks of rock-forming minerals. TotBlocks is a low-cost visualization tool that relates mineral properties (habit, cleavage, and symmetry) to crystal structures.