Help me figure out what kind of rock this is! I work in a geology lab at a museum (even thought I am not a geologist) and got a call from a man asking to help identify a rock. Since none of the geologists were in, I thought I would give it a try, since I have some background in geology. I think it's a pumice rock fuzed with obsidian. WHAT DO YOU THINK!?! Help me identify this rock!