I recently did this science experiment with the kids in my Cub Scout group. One of the Scientist badge activities is to have them grow crystals. I read a tutorial on Martha Stewart's website showing how to grow a geode using egg shells. Their scientist used alum powder, which is easy to find at most grocery stores...but can get expensive if you're planning to make a lot of eggs. You can get similar results for a lot less when you use the common ...
