It’s easy to make your own crystal geode using an egg shell and salt, plus it takes a lot less time than waiting for Mother Nature to make a geode.
About Geodes
Geodes are natural rock formations that often take millions of years to form, as minerals crystallize in cavities in the stone. The kind of geode you can make still consists of minerals, but it takes a lot less time to grow the crystals.
Salt Crystal Geode Materials
You only need a few kitchen ingredients to make a salt crystal geode:
- Salt (table salt, rock salt, Epsom salts, etc.)
- Boiling water
- Food coloring (for colored crystals)
- Egg shell
- Small bowl
Make the Geode
A natural geode forms when crystals deposit inside another mineral. Your mineral is the calcium carbonate of an egg shell.
- To get the base for the geode, crack open an egg, remove the egg, and keep the shell. Rinse out the shell and let it dry.
- Find a small bowl or cup that is bit larger than your egg shell.
- Boil enough water to fill the bowl. An easy way to do this is to fill the bowl with water, empty the water into a glass measuring cup, and microwaving the water until it boils.
- Make a saturated salt solution. Stir salt into the boiling hot water until no more salt will dissolve. You’ll know you have a saturated solution when a few crystals remain at the bottom of the container. The solubility of salt depends on temperature, so it’s best to use boiling hot water.
- If you want colored crystals, add a few drops of food coloring to the solution.
- Place the egg shell in your container. Pour the salt solution into the shell. It will overflow the shell, which is fine. Pouring the solution into the shell keeps it from floating.
- Crystals start forming as the solution cools and water evaporates out of the container. You may get good crystals overnight, but usually it takes a couple of days to see good growth, depending how saturated your salt solution was.
- When you are pleased with the crystals, remove the geode from the liquid and place it on a paper towel to dry.
- Display your crystal geode or wrap it in paper if you wish to store it. You can dust it, but don’t expose it to water or your salt crystals will dissolve.
Tips for Success
- While an egg shell is a handy and inexpensive source of natural calcium carbonate, you get more freedom in selecting your geode shape if you use plaster of Paris, which is calcium sulfate.
- For colorful crystals, use a lot of food coloring. The dye stains the egg shell and usually does not incorporate into the crystal structure. The color shows through the translucent crystals.
- Salt crystals, no matter which type you use, are hygroscopic. In other words, they readily pick up water. So, cleaning the salt crystal geode is a challenge. If you preserve the crystals with a coating of epoxy resin or polyurethane spray, you make them waterproof!
- Most types of salt have a low solubility in water. Use boiling water for making the initial solution or else it won’t be saturated and you won’t see crystal growth.
- Slow cooling and evaporation yields large crystals, while quick cooling and evaporation produces crystals quickly.
- Different salts have different crystal shapes. Table salt (NaCl) produces cubic crystals, but not all salts have this structure.