What I find really spooky about this particular sample is that it has a story to tell, recorded in that big black mark. It's suspiciously femur-shaped.
|Femur figure courtesy of Gray's Anatomy, via Wikimedia Commons.|
When this pumice flow lobe came into contact with the vegetation in this area, it was hot enough to scorch it, and in a lot of cases the pumice clasts are still resting on the tree limbs they burned. This particular piece of pumice records the shape of one of those limbs.The scorch mark itself is pretty cool - it's sooty from the carbonized wood, but it also has little patches of remelted glass.