We did this in my classroom this week. Give each child a mixture of milk
chocolate chips, white chocolate chips, and peanut butter or butterscotch
chips. These represent rocks. Let each child pour the rocks in a covered
container and shake it up to weather the rocks. Now you have sediment.
Pour the sediment into plastic baggies and give it a gentle press. You
have made a sedimentary rock. Now, squeeze and press the baggie with
lots of pressure. That makes a metamorphic rock. At this point, you are
supposed to gather up all of the metamorphic rocks and melt them in a
crockpot or microwave to represent magma. I didn't want everyone sharing
germs, so I let them eat their own metamorphic rock and melted another
bag of chocolate chips. Pour the magma into molds or spread it on waxed
paper to cool. Now you have made an igneous rock.