As an aid for teaching phase equilibria to undergraduate students of igneous and metamorphic petrology, we have designed a laboratory exercise that allows them to create a phase diagram from data produced by differential scanning calorimetry. By preparing and analyzing samples of naphthalene and phenanthrene, students acquire hands-on insight into thermodynamics and the melting behavior of pure samples versus mixtures, and ultimately create a binary phase diagram analogous to the system diopside-anorthite. In the process, students gain exposure to modern analytical instrumentation and practice quantitative skills such as calculation (e.g., calculation of weight % from molecular %), graphing, and assessment of error. Assessment of the effects of this laboratory exercise suggests that it improves student understanding of phase diagrams and the nature of reactions between crystals or between crystals and melt in metamorphic and igneous rock-forming environments.