Chocolate Rocks!

All rocks are one of three basic types - igneous, sedimentary, or metamorphic.  Even though these words sound complicated, it is really pretty easy to see what they mean, by modeling what happens when different types of rocks are formed.  And, even though we could do that with clay or playdough, it is much more fun to do it with something we can eat!  Let’s make some chocolate rocks!

Click and expand the tabs below to get started.

what you'll need

• Either white chocolate chips and milk chocolate chips OR colored baking chips (NOT M&Ms - they don't work)
• Aluminum foil
• Small microwave-safe bowl
• Butter knife
• A freezer OR a cooler with ice
• Microwave oven
• Something heavy, like a book

experimental procedure

1. Pour a few tablespoons of either milk chocolate chips or the mini baking chips into the microwave safe container.  Put them in the microwave for ten seconds.  Take them out, stir them around with the knife, put them back in, and heat them for another ten seconds.  Stir again.  If the chips are runny at this point, continue to step 2.  If they aren’t, microwave them once more for ten seconds, stir, and then go on to step 2.  NOTE: It is important to only microwave the chips (whatever kind you are using) for a few seconds at a time, otherwise they will burn and stink and you will have to start over.
   
2. Tear off a piece of tinfoil and spread it on the table.  Carefully pour the melted chocolate on the tinfoil.  What do you notice?  Are there bumps?  Are all of the chips melted, or are there still some that are in bigger pieces?  Spread the chocolate out so that it is in a fairly thin layer on the tinfoil, and then carefully put the tinfoil in the freezer or the ice chest.  Wait about five minutes, or until the chocolate is not runny.
   
3. Carefully peel the chocolate off the tinfoil.  Save the tinfoil - you will need it again in a minute.  What do you notice?  Is all the chocolate the same color?  Is it all the same thickness?  This represents igneous rock.  Igneous rocks form when magma (melted rock from underground) cools.
   
4. Break up your igneous rock (chocolate) into pieces.  Igneous rocks can, over time, erode, or break up, into pieces. Now, add some white chocolate chips (if you are using them) or some more of the mini baking chips (if you are using those).  A tablespoon or two of the chips is plenty.  
   
5. Fold over the tinfoil on itself, so that the chocolate is between two layers of tinfoil.  Press down on the chocolate.  Sedimentary rock is formed when broken pieces of rock are compressed together over time.  Carefully peel back the tinfoil, and look at the sedimentary rock you have made.  How is it different from the igneous rock?  Is it the same in any way?
   
6. Now, break up your sedimentary rock and put it back in the microwave safe container.  Heat it in the microwave again for ten seconds.  Stir, and heat it again for ten seconds.  Then, pour the chocolate onto the tinfoil again.
   
7. This time, spread the chocolate out, fold the foil over on itself, and put a heavy book or something similar on the foil.  Let it sit for five minutes, and then put it in the freezer for five minutes.
   
8. When time is up, take the foil out of the freezer and carefully peel it back. How is this chocolate rock different than the first two?  This is a metamorphic rock, which is made with heat and pressure.  Metamorphic means “changing”, and real rocks of this type have changed, due to heat and pressure.  Does your chocolate look like it has changed in any way?
   

what's happening

All rocks on Earth are made in one of these three ways - either by melted rock cooling (igneous), by pieces of broken rocks being compressed together (sedimentary), or by rocks being compressed and heated (metamorphic).  This is called the rock cycle, because a rock could start out as an igneous rock, be broken into bits by wind and water, be compressed and turned into a sedimentary rock, then be buried deep underground by an earthquake or other natural disaster, and then be changed into a metamorphic rock.  Scientists called geologists study the different types of rocks and can tell, just by looking at a rock, if it is igneous, sedimentary, or metamorphic, based on how it looks and where it is found.

variations and related activities

Since the rock cycle takes millions of years, it is much easier to model it with other things, rather than using real rocks!  Here are some other ways to understand the rock cycle and how it works.

This experiment is adapted from an experiment that we posted on our Facebook page July 17.  Here is the link to the original, from the Fernbank Museum:  https://youtu.be/7UDjqOe9arU

Here’s one that uses crayons:  https://littlebinsforlittlehands.com/crayon-rock-cycle

Here’s another one, using Starburst candy.  Notice - this one needs adult help, because it involves melting the candy:  https://lemonlimeadventures.com/edible-rock-cycle-for-kids/

This one uses either grated chocolate, or grated crayons (don’t do both together!):  https://www.mos.org/sites/dev-elvis.mos.org/files/docs/education/mos_geology-rock-detectives_diy-rock-cycle.pdf

references and links to more information

This article has simple, kid-friendly language about rocks and how they form:  https://www.ducksters.com/science/rocks.php

This article, from National Geographic, is very clear and concise. [NOTE: You might have to sign up for a free National Geographic membership to view this one]:  https://www.nationalgeographic.com/science/earth/inside-the-earth/rocks/

​If you’d like to jazz it up, here is the same information in a rap song:  https://youtu.be/G7xFfezsJ1s

The Colorado School of Mines in Golden has a very cool museum, which teaches about geology in a number of neat ways.  Of course, they are closed right now, but they do have kits which are available for checkout, if you want to learn more!  Check it out here:  https://www.mines.edu/museumofearthscience/

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