Geodes are geological rock formations in sedimentary and certain volcanic rocks. They have cavities with internal Crystal formations. In Geology these cavities are called vugs.
In this case the interior contains only quartz crystals. It is common to see more than one kind of deposit.
Isn't it a cool thing to own a rock from the other end of the globe in your hands?
Always handle rocks & crystals with care. Keep them away from little ones so they don't get hurt in any way.