Shave crayons to make different "minerals", then compress and melt them to form "sedimentary" and "igneous" rock.
Science content (2016 curriculum):
Earth/Space: Rock cycle, Earth Materials, Natural resources (5)
Science topic (2005 curriculum connection):
Earth and Space Science: Renewable and Non-Renewable Resources (grade 5)
Earth and Space Science: Earth's Crust (grade 7)