Geodes are beautiful rocks that on the outside appear quite plain. Shaped like spheres or eggs, they are found in natural hollow areas of soil or in the bubbles of volcanic rock. Over time, the air trapped within these stones forms a cavity. As minerals and ground water fill up these spaces, they begin to crystalize, so when you crack open a geode you see the beautiful deposits therein.  

STEM learners can mimic this crystallization process with eggs and form their own set of colorful “rocks”! Parental supervision is recommended, especially for the hot water part of this experiment.

What You’ll Need: 

  • 6 Eggshells (crack the eggs in half, then gently rinse out any extra egg residue)
  • Epsom salts
  • 1/4th cup of hot water
  • Food coloring
  • Empty egg carton

What to Do: 

  1. Dry the rinsed eggshells and place them in the egg carton
  2. Warm 1/4th cup of water until it is hot – but not boiling. Then add 1/4th cup of Epsom salts into it and mix until dissolved.
  3. Add more Epsom salts until they stop dissolving, then gently pour a bit of the mixture into each of the eggshells. Make sure some of the undissolved salts get into each one.
  4. Choose your favorite food coloring and add it at this stage or leave it clear.
  5. Place the eggshell carton into the refrigerator and wait for it to cool for about 3-4 hours. Drain any excess liquid. (For more intense crystallization, leave the egg geodes in the fridge for longer).

What is Happening: 

The process of geodes forming their mineral deposits happens through a process called sedimentation. This is where the particles – or the solute – are suspended in a solvent or fluid. Over time, the solutes concentrate and fuse. In this experiment, the Epsom salts are our solute. Salt water is an oversaturated solution that allows crystals to form as the water evaporates.  

Want to learn more?

My First Lab has been a leader in developing STEM equipment for the past 30 years. With products ranging from microscopes and bundles to prepared slides and accessories, we are sure to have any product for the junior investigator, hobbyist or educational leader. Learn how to create some hands-on experiments through our Maximum Launch, enjoy our blog or browse our award-winning products.