Despite the fundamental importance and increasing use of X-ray crystallography for structure determination of molecular systems ranging from metals and minerals to complex biomolecules, chemistry undergraduates receive little to no laboratory experience in X-ray diffraction.  Consequently, we have designed for the advanced undergraduate laboratory an X-ray diffraction experiment exploring crystal structures of TiO₂, an important industrial material.  TiO₂ has two common tetragonal polymorphs, anatase and rutile, for which the diffraction patterns are more complicated than the simple cubic geometry usually examined but still relatively simple compared to larger molecules.  Furthermore, diffraction measurements on powder and single crystal samples allow students to experience the advantages and limitations of the two techniques.  Depending on equipment and time restraints, possible experiments run the gamut from analysis of dry lab powder pattern spectra of mixed anatase/rutile compositions to determining the structure of rutile from measurements on a single crystal.