I just did an pretty darn good rock cycle review for the fourth grade class using crayons. It was a great model of the rock cycle and very hands-on. Here's a short summary:

1. Melted several similar colored crayons to a piece of wax. (Earth's crust with different minerals) 2. We weathered the crayon-wax structure (crust) by breaking off the crayons. 3. The crayons were weathered and eroded more using scissors and pencil sharpeners 4. We examined the soil grains for clay, silt, and sand 5. We decided what kind of sedimentary rock we wanted to create and changed our sediments accordingly (most groups picked slate, but we had one conglomerate ->this group added some chunks) 6. We placed organic things (unused slices of chapstick) in our sediments just under the surface of sediments 7. Then we applied pressure by placing wax paper over sediments and pressing with a book 8. We observed the fossils (looked better in the slate groups) 9. Then we applied even more pressure and a small amount of heat (with lighter) just for affect 10. Discussed what kind of rocks we were 11. Finally, took metamorphic rock to the center of the earth (hot plate) 12. The rock was melted into magma and then removed and poured onto another foil plate as lava 13. The lava cooled and formed an igneous rock

We stopped there, but you could start over and do it all again if you weren't sick of wax. :oD