This activity modifies a typical density laboratory exercise to fit within a lecture session. Students are asked to compare the densities of six different rocks/minerals collected from six different environments. Based on the brief description of each rock the students are asked to first predict which rock has the highest density and which rock has the lowest density. The students are then asked to construct a hypothesis and test their hypothesis by calculating the density of the rocks. Students are then asked to apply information from lecture to place each rock in the appropriate layer of the Earth.