How to Make Crystal Geode Rocks

Instructions

1. First, empty the eggshells. Crack an egg gently against the side of a bowl. Using your finger, widen the crack in the shell, and then carefully break the shell into two pieces. It doesn’t matter whether the shell is divided lengthwise or down the middle. Keep the eggs to make scrambled eggs for breakfast, or make a frittata for dinner!
2. Under warm running water, gently rinse the eggshells. Using your fingernail, scrape away any membrane left on the inside of the shells and discard.
3. If you would like your shells to have some color, dye them with Easter egg dye (just follow the directions on the package, but note that you will be dyeing the shell instead of the whole egg). Or, add about 10 drops of food color to a bowl of water and submerge the shells in the tinted water. Once the shells are colored to your liking, remove from water to a towel and allow to dry completely.
4. Next, you will “seed” the shells to give the crystals something to grow on. Squirt a dime-sized amount of glue into an eggshell. Spread the glue over the entire inside of the shell with your finger. Repeat with the other shells.
5. Place the shells — glue side up — on a plate and sprinkle with Epsom salt. Try to get all of the glue coated in the salt. Allow to dry for several hours.
6. Once the glue is completely dry, you can make the Epsom salt solution. Heat 1 cup of water in a microwave-safe bowl to boiling. Remove from microwave (use hot pads!) and stir half a cup of Epsom salt into the water. Continue stirring until you see no more crystals. Next add 1 tablespoon Epsom salt and stir until dissolved. Continue adding the salt 1 tablespoon at a time. You may have to return the bowl to the microwave and reheat for about 30 seconds after each addition of salt because the water temperature will start to cool. Repeat until you can no longer get the salt to dissolve completely. I used 6 additional tablespoons.
7. Place the shells — salt side up — in an empty egg container. Ladle the Epsom salt solution into each shell, filling to the top. Be sure to put the solution into the shells quickly, because if the water cools too much, the salt will fall back out of the solution. Before adding the salt solution to your egg shells, give it a quick stir and if you see any crystals in the bottom of the bowl, heat for 30 seconds and stir to dissolve the salt. Add one drop food color into each shell and stir with the end of a spoon or a toothpick to distribute the color. 
8. Set the egg carton and shells aside to dry. Check them a couple of times a day. If a thin, hard layer forms across the top of the liquid surface, you can break the dry layer to hasten the evaporation process. Depending on the environment, you will have “geodes” in 1 to 3 days!