In this inquiry-based activity, the usefulness of thin-layer chromatography (TLC) to visualize the difference between spearmint and peppermint is explored. The experiment may be used in any class where TLC is discussed from high school to college. We have used this activity with science majors in an organic chemistry laboratory, with non-science majors in a brewing science class, and in a general science class for elementary education majors. The experiment can be completed in a two-hour period. R-(-)-Carvone and (1R,2S,5R)-(-)-menthol are responsible for the cool and minty sensations associated with these plants. These observable properties and the structural formula of the compounds provide the basis for a good discussion on structure-activity relationships. (Contains 3 figures and 1 table.)