Geodes are small rock cavities lined with crystals or minerals. They form through sedimentation, a process in which particles (solute) are suspended in fluid (solvent) and then accumulate. (Here, the Epsom salt is the solute, and the water is the solvent.) The salt particles fuse together because the water is so saturated, forming crystals as the water evaporates.
What You'll Need:
1. Help kids crack an egg at the narrow end and carefully widen the opening to the size of a quarter. Empty into a bowl; repeat with more eggs. (Save the yolks and make a scramble or frittata for lunch!)
2. Set shells in a bowl of hot water to rinse. Then show kids how to gently rub their thumb on the inside to loosen and remove the membrane (there may be two layers). Turn the shells over on a towel to dry. If desired, dye them before the next step (follow instructions on the box); let dry.
3. Set the shells inside the carton. Brush the entire inside with a thin layer of glue and dust with Epsom salt (this will act as a starter crystal). Let dry completely (a few hours).
4. Boil 1 cup water and remove from heat (an adult’s job). Slowly add ½ cup Epsom salt and stir until it’s dissolved. Continue stirring in small amounts of salt (a tablespoon or two at a time but no more than ½ cup) until it no longer dissolves, then STOP. You’ve made a super-saturated solution! It should be thick but not slushy.
5. Carefully pour the solution into your shells with a small ladle, filling to the top. Add a drop of food coloring to each egg, and stir gently with a toothpick. Place your shells somewhere safe and at room temperature.
6. Check your eggs daily. If you find a thin, hard, jagged layer forming on the surface, gently break it up with a toothpick (allowing the water to evaporate). After a few days, all the water will evaporate, leaving colorful geodes behind!
Bonus Fun: Have your child experiment with other soluble solids, like sugar, baking soda, or table salt—does she get the same result?