How to grow your own geodes

Create crystals inside eggshells to make these wonderful geode-like structures at home

1.Break the egg

First, you need to carefully break some eggs as close to the narrow end as you can manage. This means you’ll have more shell to use as the container for your geodes. You’ll need to get your finger inside the egg to clean it out though, so don’t make the hole too small. Around two or three centimetres across will work nicely, but if your hole is bigger it should still work.

2.Clean it out

Now you need to clean the inside of your eggs. Pour hot water inside the empty shells – this cooks any of the egg white that may be left inside. Now tip the water out. You should be able to pull the white and any remaining egg membrane out of the egg with your finger. Make sure you get it all – if you leave any in there it might grow mould, which will make your crystals turn black.

3.In the tray

Place the shells in an egg carton lined with wax paper, or in a mini muffin tin with some cotton wool in the bottom. The key is to keep your eggs upright so that you can pour in the liquid and let it dissolve slowly to form the crystals. Once your eggs are upright, boil some water in a kettle or a saucepan, then pour it into a coffee mug until it’s about half full.

4.Make your solution

Now you can add a solid. Table salt, rock salt, sugar and baking soda should all work, so you can try a few options to see which gives the best result. You need to add a solid and stir until it all dissolves. Start with about a quarter of a mug full, then slowly add more until it’s saturated. Now add a few drops of food colouring to your mixture.

5.Let them grow

Place your carton or tray of eggs somewhere safe where they won’t be disturbed. Carefully pour your colourful solutions into the shells, filling them as close to the top as you can. Leave them alone until all the water in the shells has evaporated. Once it has you’ll see crystals inside your eggs, just like those you’d find in geodes.


This article was originally published in How It Works issue 115, written by Stephen Ashby


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