As part of its ongoing efforts to promote all things related to the beloved Pokémon franchise, The Pokémon Company has shared special content dedicated to Onix:
[Official] Iwark Diorama | Nishi
Did you know? As Onix digs through the ground, it absorbs many hard objects. This is what makes its body so solid. It rapidly bores through the ground at 50 mph by squirming and twisting its massive, rugged body.
Source: The Pokémon Company