We used 3D-printed building blocks (TotBlocks) in an undergraduate optical mineralogy lab session to illustrate the links between crystal structures and the properties of minerals. Students built mica, pyroxene, and amphibole structures. We observed an improved understanding of cleavage (how minerals break) and pleochroism (how light interacts with minerals), but understanding did not improve with more abstract concepts. TotBlocks hold potential as a teaching tool in mineralogy classrooms.