Geodes are very interesting. Geodes start their lives as a hollow bubble inside a layer of rock. The bubble could be from air inside volcanic rock or it could come from the hollow remains of animal burrows or tree roots. These rocks form from air bubbles inside of volcanic rock.
Rains hits down on the hot bubble, the chemicals in the rock are slowly released into the water. Some of the water soaks through the rocky outside of the bubble and is trapped for a moment on the inside. As the mineral rich water moves through the bubble, tiny crystals are left behind, sticking to the sides of the bubble. Millions of years pass while this in and out flow of water gradually builds crystals inside the empty space. Pretty neat huh?
You can find geodes anywhere! They have a very ugly exterior but once broke open they are so beautiful in the inside.