Rocks are so fascinating to my boys. They both have collections of their favorite rocks at the head of their beds. We have river rocks that border almost the entire perimeter of our house. This past summer, the boys spent hours choosing their favorite ones and carefully lining them up on a brick ledge along the front of the house...one rock per brick. That collection stayed there for months. Sometimes someone would discover a rock that was deemed better than one in the collection, and there would be an exchange. I loved when people would ask about the rocks and the boys had a chance to show off their favorites.