"Geodes are pockets of crystals that form in sedimentary and igneous rocks. They start as hollow spaces in rock that is porous enough for water to seep through. The water carries dissolved minerals, which are deposited in the open space, forming a lining of crystals. Most geodes contain quartz crystals, but they can also contain calcite, celestite, and other minerals. "My son had Earth Science last school year and studied rocks so this was another great ad on to what was taught in the K-12 program, we love his teacher he has his year, she currently teaches a few levels of Science. I only hope that they can let us have her again when he moves up to 8th next fall. I have to admit between the two kids, it took two trials and errors.but that is what learning is about. I have to say that my ninth grader didn't put in a spoon over night like my son did his and his had crystals. He thinks that this was the variable that may have made it work for him. We are going to do it again, however they are going to separate the egg halves and place Epsom Salts in place of Alum like the kids did for this project, and a spoon in one container and not the other container. I will get back to you when this happens. Again, if you would like some really great ideas for Science you can either hop over to my blog pal at http://littlemisshypothesis.blogspot.com/ or the Steve Spangler site. Have a great day.