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Salt Crystal Geode

Sodium Chloride Crystals in a Geode


This salt crystal geode was grown on a piece of eggshell.

This salt crystal geode was grown on a piece of eggshell.

Anne Helmenstine These are salt crystals that grew on the inside of a bowl.

These are salt crystals that grew on the inside of a bowl. The coloring is from food coloring that was added to the salt solution.

Anne Helmenstine
You can make a salt crystal geode in any color of the rainbow. The geode showcases the beautiful cubic structure of sodium chloride or table salt.

About Geodes

Geodes are rock which contain a core of crystals. Normally, millions of years are required for flowing water and minerals to deposit crystals. A geode you make yourself is still made from minerals, but you can use evaporation to speed up the process of crystal deposition.

Salt Crystal Geode Materials

  • salt
  • boiling water
  • food coloring (if you want colored crystals)
  • eggshell
  • small bowl or cup

Prepare the Geode

A natural geode forms inside a mineral. For this project, the mineral is the calcium carbonate of an eggshell. Carefully crack open an egg, discard the egg, and keep the shell. Clean the egg from the shell. Try for a clean break, to create two halves of the shell. If you want a rounded geode you may wish to just remove the top of the shell.

Grow a Salt Crystal Geode

  1. Select a bowl or cup that is just a little larger than your eggshell. Boil enough water to fill this container.


  2. Stir salt into the boiling hot water until no more salt will dissolve (crystals start to appear at the bottom of the container). Hot tap water is not sufficient for making the solution.


  3. Add food coloring if colored crystals are desired.


  4. Set the eggshell into the container. Pour the salt solution into the shell. It will overflow the shell and fill your container. Try to avoid getting undissolved salt in the eggshell or container.


  5. Set the container someplace where it won't be disturbed. Allow the solution to evaporate. Crystals will start to form over the course of a few days. You can remove the geode whenever you are pleased with its appearance and allow it to dry. The largest crystals will result from allowing the solution to fully evaporate, which could take a few weeks, depending on the humidity level in your home.


  6. You can display your crystal geode or you can wrap it in tissue paper or a paper towel to store it.

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