This homework assignment gives students first-hand experience with thermobarometric calculations. Because many of my students are math challenged, I give them a choice of solving the equations by hand or with Excel. They must first look at mineral compositions and make predictions regarding relative pressures, then calculate conditions for two sets of compositions, and finally use the P-T results to evaluate a tectonic hypothesis. The "thinking" questions are very open ended and can involve discussion of diffusion, heat flow, and tectonic settings.