Geodes, seemingly ordinary rocks hiding pockets of crystals inside, have fascinated amateur geologists for centuries, but did you know you can make your own geodes with just what’s in your kitchen?
Something to hold the eggs (a piece of the carton works well for this)
Water-soluble solid (salt, sugar, baking soda, etc.)
Crack eggs as close to the narrow end as possible to save as much shell as you can
Heat water to nearly boiling and pour it into the egg, cooking the membrane inside so you can remove it. (if you don’t remove the membrane, it will mold and turn the crystals black)
Bring your water to a boil in the saucepan, gradually adding about half as much salt by volume as you have water
Keep adding salt until no more dissolves into the water
Add the mixture to your eggshells
Add the food coloring to each egg
Wait a few days for the water dissolve
Admire your results
So how does this exactly work? When you’re boiling the water, you’re adding energy to it in the form of heat, allowing it to dissolve more of the solid than it normally would. At this point, there’s so much solid (in our case salt) dissolved in it that there’s nearly no space left between molecules. This now “super-saturated” solution gradually loses energy as it cools down, forcing the solid out of solution slowly. This slow release allows the solid to instead build a growing network of crystals inside and outside the eggshell. This is actually a similar process to how geodes form in nature: water with dissolved minerals seeps into air pockets inside rocks, slowly depositing the minerals as the water flows through the rock. Try it for yourself!