Can anyone help me identify this unusual rock?

My dad found this while prospecting and were unable to identify what it's made up of. It was obviously molten, at one point, as suggested by the cavity inside, the bumpy texture, but also there's what appears to be some sort of glassy. crystalline structure protruding from the outer surface. If anyone can tell us what this is made of and how it ended up in a dry creekbed in central Arizona, I would appreciate it greatly.