How to Grow Glittering Crystal Geodes in Eggshells

Part craft project and part science experiment, this hands-on crystal-growing activity will fascinate your kids.

Colorful Egg Shell Geodes

Colorful Egg Shell Geodes

Photo by: Debbie Wolfe

Debbie Wolfe

Crystals are fascinating for adults and children alike. While it takes thousands of years for crystal-filled geodes to form in nature, you can grow your own crystals in a day with supplies found at the grocery store. This sparkling eggshell geode is a delightful science experiment that your kids will love.

What You'll Need

  • 3/4 cup plus 2 tablespoons of alum powder (located in the spice section or canning supplies section of your grocery store)
  • egg
  • 2 cups hot water
  • school glue
  • paintbrush
  • food coloring
  • 2 cup glass measuring cup
  • small glasses or pint canning jars

Photo by: Debbie Wolfe

Debbie Wolfe

Crack Egg Lengthwise

First, you'll need to crack the egg. You can crack them in half crosswise like normal if you like. However, to make them look like real geodes, they need to be cracked in half lengthwise. The easiest way to do this is to blow out the egg first, then use a pair of scissors to cut the shell lengthwise.

Glue Alum Powder to Eggshell

After you cut the shell, wash it and wipe it dry with a paper towel. Next, dump about two tablespoons of alum powder into a bowl. Drip some glue into the shell halves and spread it all over the surface of the inside of the egg with the paintbrush. Generously sprinkle the alum powder on the wet glue. (If you want the crystals to grow on the edges of the shells or slightly on the outside, you'll need to glue alum powder in those areas as well.) Turn the shell halves over and gently tap out any excess alum. Place them on a paper towel to dry overnight. Don't skip this step — the alum powder needs to be completely dry to provide a surface for the crystals to adhere.

Photo by: Debbie Wolfe

Debbie Wolfe

Dissolve More Alum Powder in Water

The next day, bring two cups of water almost to a boil and pour it into a large measuring cup. Add the 3/4 cup of alum powder and stir until it's mostly dissolved. You may have a bit of sediment at the bottom of the cup. Divide the mixture into two small glasses or half-pint canning jars.

Photo by: Debbie Wolfe

Debbie Wolfe

Add Food Coloring

Next, add 20 to 30 drops of food coloring to each jar and mix. Let the mixtures cool for 30 minutes.

Photo by: Debbie Wolfe

Debbie Wolfe

Soak Eggshells in Alum Solution

Finally, place one shell half into each jar alum-side up. Gently push the shells to the bottom of the solution with the spoon. Allow them to sit there, undisturbed, for 12 to 15 hours.

Photo by: Debbie Wolfe

Debbie Wolfe

Remove Shells From Solution

After 12 to 15 hours, your alum crystals will have grown! Carefully remove the shells and place them on a paper towel to dry and finish the geode-creation process. If you want bigger crystals, let the shells sit in the solution longer.

Eggshell Geode

Eggshell Geode

Photo by: Debbie Wolfe

Debbie Wolfe

Now for the science behind the alum geode-growing process: The geode is formed through a process called sedimentation. Adding the alum powder to the hot water created a supersaturated solution. This simply means that there are suspended particles of alum powder in it, and as the solution cools, these particles of alum begin falling to the bottom. As the alum particles settle on the bottom, they begin crystallizing. Other substances like Epsom salt, sugar and borax also crystallize, but I've found that alum powder makes the best crystals.

Egg Shell Geodes

Egg Shell Geodes

Photo by: Debbie Wolfe

Debbie Wolfe

More Kid-Friendly Science Experiments

See All Photos

Shop This Look

Next Up

How to Make Paper Pinwheels

Use old book pages, flash cards, scrapbook paper or even sheet music to make these sweet pinwheels that can bring a festive, playful touch to parties and holidays. They're a snap to make so you can whip up an entire bouquet of them to display in flowerpots, baskets, buckets or pitchers.  

How to Make Shell Tiaras for a Mermaid

Every mermaid deserves a crown. Learn how to craft this inexpensive headpiece for an underwater-themed party or for an accompaniment to a Halloween costume.

22 Fun Kids' Crafts for Cold Winter Days

Beat cabin fever with creativity.

DIY Kid's Flamingo T-Shirt

Plain white tee no more! Sass up any run-of-the-mill top with a little paint and 3D pompom magic.

Science for Kids: 2 Ways to Make a Cloud in a Jar

Amaze your kids while teaching them how clouds form in the atmosphere with this easy experiment.

Break a Leg! DIY Doorway Puppet Theater

Give your kids a taste of the spotlight without leaving home.

Kid-Friendly Craft Project: Salad Spinner Art

Get crafty with paint and a salad spinner and make colorful works of art with your little ones. Spin art is perhaps the most fun, well-contained type of mess that you can make — even toddlers can easily participate. Consider this activity on a rainy day or during arts and crafts at an outdoor summer camp.

DIY Glow-in-the-Dark Chalk Spray for Instant Summer Fun

This is one summer project your kids will actually want to do.

5 Paper Towel Roll Crafts for Kids

Recycling has never been so creative and simple. New worlds can be explored, creatures created and races won simply with the help of a paper towel roll.

Washable Crayon T-Shirts for Kids

Help kids create t-shirts they can color again and again after every washing.

Go Shopping

Refresh your home with stylish products handpicked by HGTV editors.

Watch Live TV

Don't miss your favorite shows. Live stream HGTV now.

Follow Us Everywhere

Join the party! Don't miss HGTV in your favorite social media feeds.