Book 27, Question 131
How can you make an eggshell geode?
Wash half an eggshell in hot soapy water with a grown-up, rinse it, and let it dry.
Then place it in an egg carton. A grown-up prepares a warm, strongly dissolved Epsom-salt or sugar solution and pours it into the shell. As the solution cools and slowly evaporates over a few days, crystals grow on the inside, a bit like a real geode. Wash your hands, keep it still, and do not eat it.