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

6 Responses to “Eggshell Crystals”

  1. Aurora Lipper says:

    It is best to remove the membrane. That way the alum can properly bond with the shell.

  2. Does it matter if the membrane is still inside of the shell or should that be removed when cleaning? Thanks!

  3. No they are different, but you can use either one. If you already have a chemistry kit, it may have copper sulfate and you may use that. Please do be careful with the copper sulfate, it is a chemical that requires special handling.

  4. dawncurran67 says:

    On the video page it mentions using alum, as well as on the overview on the print out. But on the print out, in materials, it mentions using copper sulfate. Is alum the same thing as copper sulfate? It doesn’t appear to be from looking it up, but I may be wrong.

  5. You can use salt, sugar, borax… slum is only one of the options. You can grow any kind of crystal in the eggshell.

  6. do we have to use alum? or can we use something else