Onix resembles a giant chain of gray boulders that become smaller towards the tail. It has a rocky spine on its head and a pair of black eyes right beneath it.
Onix evolves into Steelix in the original games, but since Steelix isn't implemented Onix cannot currently evolve.
Onix can not be found in the game, it can only be seen at 1st gym (as brocks pokemon) Though the only way to find Onix is use of a hacking tool such as Cheat Engine. Luckily there has been a patch to Cheat Engine but not Art Money.