Geodes are formed from gas bubbles in flowing lava. Up close, a geode is a crystallized mineral deposit that is usually very dull and ordinary-looking on the outside.  When you crack open a geode, however, it’s like being inside a crystal cave.  We’ll use an eggshell to simulate a gas bubble in flowing lava.

We’re going to dissolve alum in water and place the solution into an eggshell. In real life, minerals are dissolved in groundwater and placed in a gas bubble pocket.  In both cases, you will be left with a geode.

Note: These crystals are not for eating, just for looking.

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23 Responses to “Eggshell Crystals”

  1. ericksonnationmom says:

    Im going to do this for Easter decorations

  2. No, pipe cleaner won’t provide the desired effect. You’ll need to use clean egg shells.

  3. ericksonnationmom says:

    would a pipe cleaner work instead of an egg shell???

  4. Great question! The crystals will form very quickly if the water is really hot or extremely saturated. Go ahead and try it both ways, then note the differences!

  5. Anni Killam says:

    what happens when you get the water too hot and too saturated?

  6. Garrison Brown says:

    If you put the solution in a oven somewhere in between 120 and 200 degrees Fahrenheit would the solution evaporate and form crystals quicker?



  7. Hmmm… I have two thoughts. Either the bulk powder you bought isn’t pure alum (there’s something else mixed in), or the solution wasn’t saturated and you just need to mix in more powder to make it work. You can heat the water so it can absorb more powder to be really sure it’s super-saturated. Let me know how it goes!

  8. andrea alfred says:

    We made alum crystals with alum powder from the grocery store and it worked fine, but later we bought alum powder from the bulk barn and have been unable to make crystals, we have tried a few times and never any crystals. Do you have any idea why?

  9. Melanie Williamson says:

    does saturated salt work


  10. Kristen Mladenoff says:

    My daughter suggested an egg carton would be a great place to store the shells while the crystals form.

  11. Fatimah Zainulabideen says:

    can i use a cup instead of eggshells

  12. You can try – or you can dissolve the shell in vinegar, but that may also wear down the crystals. Try it?

  13. Ronald Hamilton says:

    Can you chip away the eggshell when the geodes have formed? Or will that mess up the geode?

  14. Do you mean the alum? It’s int he spice section or the gardening area.

  15. Diane Salcedo says:

    can you by it at target?

  16. It’s just a place to grow the crystals in. 🙂

  17. Laura Swick says:

    I didn’t try this but I’m going to is the eggshell special? I mean does the aluminum chemically bind with the aluminum or is it just a place to keep the crystals.


  18. Crystals start growing when the molecules in a liquid cool down and harden. Molecules in the liquid attach together as they cool, and when they form a repeating pattern, it’s called a crystal. In nature, crystals form when magma cools slowly. Crystals also form when water evaporates, like with salt crystals.

  19. Patricia Stone says:

    why do the crystals form

  20. We heat it up to dissolve the crystals into the solution, so just warm it up until the bits on the bottom are gone.

  21. Kerry Marsh says:

    How warm does it need to be?