STEM Activity: Crayon Rock Creations

If you close your eyes and think of a volcano, what do you picture? If it’s piping hot lava, we have a fun fact for you. Did you know that magma and lava are actually liquid, molten rock?

Molten rocks can be categorized by texture, how quickly they cooled and where they were formed. When molten rock cools and becomes solid, the result is an igneous rock.

There are two types of igneous rocks: extrusive and intrusive. Extrusive igneous rocks cool quickly and solidify on or above Earth’s surface. Intrusive igneous rocks, on the other hand, are formed if molten rock cools slowly and solidifies below Earth’s surface.

You can explore the difference between these two types of igneous rocks using your old crayons! In this hands-on experiment, you’ll mimic the formation process and notice the unique qualities of each type of rock. Let’s get started!

Materials Needed

• Aluminum foil (two large sheets)
• Bowl or plate
• Bowl of ice water, large
• Cheese grater
• Crayons (three or more different colors)
• Dish towel or potholder
• Frying pan, medium or large
• Oven mitts or tongs
• Stovetop or hot plate
• Wood toothpick or popsicle stick

Step-by-Step Instructions

This STEM activity uses a cheese grater and requires a hot plate or stove. As you follow these step-by-step instructions, adult supervision is important for a safe creation process. Ask a grown-up to join you as you bring your crayon rocks to life!

1. Using a cheese grater, shave your crayons into tiny pieces above a plate or bowl.
    
2. Form two bowls with each sheet of aluminum foil by folding and pinching the edges. Make sure each bowl fits inside your frying pan and the bottoms of the foil bowls are flattened (like a pie!).
    
3. Sprinkle half of your crayon shavings into each foil bowl.
    
4. Place one foil bowl with crayon shavings in the frying pan.
    
5. Heat the frying pan with the foil bowl on the stovetop or hot plate over medium heat and watch the shavings melt. Once the shavings have fully melted, turn off the heat. This is your molten rock!
    
6. Using oven mitts or tongs, carefully remove the foil bowl from the pan and set it on a dish towel or potholder to cool.
    
7. While your molten rock cools, place several ice cubes into a large bowl and add several cups of cold water. Set the bowl of ice water to the side.
    
8. Follow steps 4-6 with your second foil bowl.
    
9. Stir the melted shavings in your second foil bowl with a wood toothpick or popsicle stick until the colors are blended.
    
10. Carefully remove the second foil bowl from the pan using oven mitts or tongs and slowly pour your molten rock into the bowl of ice water. What do you notice?
     
11. Once all the molten rock is poured into the ice water, remove the solidified piece from the bowl. This is your extrusive igneous rock!
     
12. Check the first foil bowl you placed on the towel or potholder. If the molten rock has completely cooled and solidified, remove the piece from the foil. This is your intrusive igneous rock!
     
13. Compare your two igneous rocks. Ask yourself:
    • What properties do they have?
    • What makes them similar?
    • What makes them different?

What Are We Discovering?

All rocks form through a process called the rock cycle. In this experiment, we explored how igneous rocks are formed when molten rock cools and solidifies.

Rocks also can form through a process called lithification, where small pieces, or sediments, of rock are squeezed together. The result is called sedimentary rock. If sedimentary or igneous rock interacts with high heat and pressure deep in Earth’s crust, it transforms into metamorphic rock. All rocks can transform into sedimentary, metamorphic or igneous rock.

This experiment with crayons echoes the work of National Inventors Hall of Fame^® Inductee Henry Bessemer, inventor of the Bessemer Process, a major advancement in steel making. Before his invention, steel was very limited, costly and made through a difficult process. Resulting in stronger steel that could be mass-produced at a lower cost, the Bessemer Process involved blowing cool air through molten iron to remove impurities, mimicking rock formation – just like your crayons!

Keep Creating

Looking for inspiration for your next colorful creation? Sign up for monthly National Inventors Hall of Fame emails to get the latest STEM experiments. We can’t wait to see you bring new ideas to life!