Ice Rock is used to evolve Eevee into Glaceon. To accomplish this, Eevee must be leveled up within 10 blocks of the rock. This rock can be found in the icy plains biome. It can be destroyed with a pickaxe, and it will drop a item called Icy Rock. You can place it down again, but it will need enough space. Otherwise, in the chat it will say "Can't place this here!"