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. This Pokémon has a magnet in its brain that serves as an internal compass. Its body absorbs many hard objects, making its body very solid. As it grows older, it becomes more rounded and smoother, eventually becoming similar to black diamonds. Onix tunnels under the ground at over 50 miles (80 kilometers) per hour, which causes tremors and a terrifying roar that echoes a long way. Onix can be found in mountains and caves, though it prefers underground tunnels with little light.