These fossilized cystoid geodes might have beautiful sparkling crystals inside. The only way to find out is to break it open. This geode is the fossilized body of a cystoid marine animal that lived attached to the ancient sea floor over 400 million years ago. The organic material decayed over time and was replaced by water rich with silica which filled the interior and allowed crystals to form inside. WARNING: USE EYE PROTECTION AND GLOVES BEFORE ATTEMPTING TO CRACK OPEN THE GEODE. Put an old sock or towel around it and then hit it with a hammer. These pieces are extremely variable in size, shape and what is inside. The pictures show a small piece of a broken one, a completely intact one and one where the end was broken off. Most pieces are like the middle one. Average size is 2.5-3.0" in diameter. This is a great gift for kids!