3 years & up. Geology gets exciting when you break open these geodes and find crystal treasures. These large size geodes break open easily. They will amaze and delight your little scientist. Hollow in the center due to crystal formations, each one contains clues about the mystery of the formation of our earth. This hands-on earth science experiment is sure to please. Each piece measures approximately 1 - 1.5" diameter. Includes 10 geodes.