Steelix resemble giant iron snakes. They are a reflective, silvery gray, which reflects the sunlight making them shine slightly. They are about 30 feet long. Their body is made up of rock-like sections, some of which have massive rock spikes coming out of them. They have a massive head mainly made up of their jaw. The jaw is large and wide with sets of large square teeth inside. Along their bottom jaw are a pair of ridges (varies with gender). Their eye sockets are slightly set in, giving them good eye protection. Underneath their bottom jaw and chin, on the underside of the jaw, there are small square domes. Their heads have two long ridges going from the eyes up to the top of their heads. Their jaws also have massive ridges where they meet their skull.
The rock portions on their body start at the back of their head. There are three slightly larger sections that have the massive rock-like spikes coming out of them. The tail ends in a long sharp point, but with a blunt tip. Steelix's rock-like sections don't look perfect and can easily be mistaken for rocks, for they have many chips and scrapes all along them from fights and tunneling.
A male Steelix has two pairs of sharp ridges on each side of its bottom jaw, one big one and one slightly smaller one. A female Steelix has only one pair of ridges on either side of its bottom jaw, each the approximate size of the male's larger ridges.
Steelix has a body that is stated to be harder than diamond. They can create Sandstorms by spinning their body in circles, and they can tighten and harden their tail to attack.
Steelix are rather rash and often charge into situations without thinking about the consequences of their actions. Often if they are disturbed they will attack anyone rather than the actual person responsible for disturbing them. They also often prone to being a bit vain and in some cases a bully to other Pokémon that happen to live in the area they are living in. This could be from evolving from Onix and realizing how powerful they have become and letting this knowledge go to their heads, as Onix are usually more peaceful than Steelix. Steelix don't give up until they are beaten. Often they are adamant about their choice of action. Steelix like to burrow underground and prefer to live inside mountains or on mountains, or even caves.
Although Steelix require an item to evolve from Onix, they can be sometimes be found in the wild, where they populate deep caverns, tunnels, and a cliffside cave in the Johto region. As they live far underground, miles from the surface, they don't often surface above ground unless provoked. It is said that when an earthquake happens, multiple Steelix are battling far below the surface.
From Steelix's Pokédex entries, it can be presumed that Steelix eat soil and boulders.
This Pokémon was unavailable prior to Generation I.