The elusive Pit OP remains one of the rarest creatures on Earth…
Darn, I forgot what board I was on.
Assuming that the OP was asking, “What’s the rarest material on Earth?” (wow, what a stretch, given the title, eh?)…
I would have to guess one of the superheavy artificial elements, created in labs, that decay in microseconds…
Neutronium, I think.
Antimatter.