I have a rock that I found while on a college class outing in Eastern Oregon. It is hollow inside and has multiple objects inside that rattle. I was told by a professor that isn't was formed when lava was ejected into the air and as it fell, it sort of ballooned out and solidified with smaller rocks inside of it. I have searched the internet and not found anything that fits this description. My guess is that it is a geode but it doesn't seem to match any of the descriptions or photos I have found. Can anyone tell me what it is?