I figured I'd have a go at a (hopefully) nice riddle.
I come from the deepest layers,
Yet am seen in the highest.
I'm made of nothing but seas,
But judged on only four of them.
I propose you think carefully about your answer,
I'm more likely to scratch your reputation than the other way around.
Who/what am I?
Note: The last lines are just part of the riddle. No need to be afraid I'll downvote every incorrect answer!
Edit: Two additional lines, since they were too nice to be left out:
Collectors and criminals covet me yet can live without,
But there's one group here that cannot be separated from me.