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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Here’s what you need:


  • clean egg shells
  • alum (check the spice section of the grocery store)
  • food dye
  • water


 
Download worksheet and exercises


This is a continuation of the Laundry Soap and Rock Candy experiments, so make sure you’ve done those before trying this one.


Find a clean half eggshell.  Fill a small cup with warm water and dissolve as much alum in the water as you can to make a saturated solution (meaning that if you add any more alum, it will fall to the bottom and not dissolve).


Fill the eggshells with the solution and set aside.  Observe as the solution evaporates over the next few days.  When the solution has completely evaporated, you will have a homemade geode.  If no crystals formed, then you had too much water and not enough alum in your solution.


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Comments

27 Responses to “Eggshell Crystals”

  1. Sure – anything that will hold your crystal solution will work just fine!

  2. Can you use something else besides egg shells?

  3. Aurora Lipper says:

    The crystals in this experiment are made from alum, so that is the only substance you can use. But you have other options for growing crystals in the other experiments.

  4. candjpatch says:

    We cannot buy alum anywhere in our town. Is there any other substance we can use?

  5. ericksonnationmom says:

    Im going to do this for Easter decorations

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

  7. ericksonnationmom says:

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

  8. 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!

  9. Anni Killam says:

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

  10. 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?

    Thanks

    -Garrison

  11. 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!

  12. 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?

  14. Melanie Williamson says:

    does saturated salt work

    -Gabe

  15. Kristen Mladenoff says:

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

  17. Fatimah Zainulabideen says:

    can i use a cup instead of eggshells

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

  19. Ronald Hamilton says:

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

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

  21. Diane Salcedo says:

    can you by it at target?

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

  23. 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.

    Liam

  24. 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.

  25. Patricia Stone says:

    why do the crystals form

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

  27. Kerry Marsh says:

    How warm does it need to be?