We brought home a few geodes not long ago after a visit to a friend's house in Indiana. As soon as we got home from our trip I couldn't wait to get out the sledge hammer and crack open those things to see what was inside. Andy laughed at me. "No, no dear. Not when I have a tile saw to cut them with."
Of course! He's a genius! You see, I never think of playing with sharp spinny things that could potentially leave me without a hand. But Andy now, he always thinks like that.
So we found out that our little geode is a type that's called a nodule. Here is a link about that for you smarties that care.
I just think it looks really pretty in there.