Does anyone else use gems?

Pearls are fascinating to me, as they seem to exist solely out of coincidence.

Then there's obsidian: something so beautiful associated with so much violence (formed by lava flow, used as weapons by Mesoamericans...). Groovy.

I have one of those obsidian arrowheads. Smooth volcanic glass. <3 But it's chipped a little and wasn't done well. What's cool is that one side sort of has some smooth grooves in it, so you can see where it finally stopped moving. What interests me more is marble and granite. You have to wonder how much force was used to push the combinations together. I always imagined the smaller portions growing in on it like mold or something. xD