Exercise 2.3: Chocolate Rock Cycle

This demonstration will show you how the rock cycle works. Normally the rock cycle works too slowly for us to observe and a lot of the changes happen underground where we can't see them. The temperatures and pressure necessary to change rocks can not easily be observed by humans. For this demonstration we will be using something that can be easily found and modified by manageable levels of temperature and pressure ...

CHOCOLATE!!!!

Materials

  • 1 bar of solid dark or milk chocolate
  • 1 bar of solid white chocolate
  • 1 cheese grater
  • Wax paper or Saran Wrap
  • Small glass bowl
  • Plastic or metal teaspoon
  • Microwave

Follow the procedure instructions below and take pictures as you go. Your final assignment submission should include: pictures of each of your different rocks and the answers to the Analysis Questions.

Procedure for Sedimentary Rock

1. Using the cheese grater, grate the bars of chocolate until they are all grated into tiny pieces. You may not need to use all the chocolate to get enough chocolate shavings for the experiment. You can save the chocolate that you don't use and eat it later. :D

2. Lay down a piece of wax paper/saran wrap that will be large enough to wrap up all the chocolate shavings.

3. Combine the two colours of chocolate shavings together until they are all mixed up. You should aim to have about 1/3 to 1/2 cup of chocolate shavings altogether.

4. Fold the paper/plastic wrapping around the shavings until it forms a flat-ish envelope that is about 10 cm x 10 cm. Make sure the package is folded tight so no chocolate can fall out.

5. Press the package flat with your hands. Press down HARD to compress it. You may need to put the package on the floor and actually stand on top of it to get enough pressure.

6. Unwrap the chocolate and take a look at your compressed sedimentary chocolate. Take a picture.

Procedure for Metamorphic Chocolate

1. Place your sedimentary chocolate into a small glass bowl.

2. Microwave your chocolate for a few seconds - just until it gets warm and a little bit soft. Every microwave has a different strength, but start off with 5 seconds on the timer and put it in for 5 seconds at a time until it just starts to get warm.

3. Lay down a piece of wax paper/saran wrap. Lay your softened chocolate rock on the surface.

4. Let the chocolate cool. This partially melted and cooled chocolate is similar to metamorphic rock. Take a picture.

Procedure for Igneous Chocolate

1. Scrape up the cooled metamorphic chocolate and put it back into your glass bowl.

2. Put the chocolate back into the microwave and heat it up until the chocolate is totally melted. This may take around 30 seconds or longer, depending on the size of your rock and the strength of your microwave. Watch the microwave to ensure the chocolate does not bubble too much or burn.

3. Take the bowl out of the microwave (careful - it's hot!) and stir the melted chocolate with your spoon until it is fully combined.

4. Lay down a piece of wax paper/saran wrap, and scrape it out of the bowl with your spoon onto the wrap. It should be a fully melted liquid.

5. Let the chocolate cool. This melted and cooled chocolate is similar to igneous rock. Take a picture.

Analysis Questions

1. Using the cheese grater to grate the solid chocolate bars broke them down into little pieces. What part of the rock cycle does this represent?

2. Why did you need to press down (or stand on top of) the chocolate shavings to create the sedimentary chocolate?

3. What was the texture of the sedimentary chocolate? Compare this to what you know about sedimentary rocks.

4. You slightly melted the sedimentary chocolate in the microwave. How are sedimentary rocks melted in real life?

5. What is the difference between the appearance of your sedimentary chocolate and the metamorphic chocolate?

6. Describe a place on Earth where igneous rock is formed.

7. The igneous chocolate is your final product for this experiment. What could you do to turn this igneous chocolate back into a sedimentary chocolate?

Remember to submit the pictures of your 3 chocolate rocks along with the answers to these questions.