Mithril Pickaxe is stronger than Steel Pickaxe and can be used for combat or to mine rocks for ore. It requires an Attack level of 20 to be equipped, and a Mining level of 21 to be used. It can be bought from Bob east of ::home for 1,300 coins.
Mithril Pickaxe can be made with the Smithing skill at level 55 using two Mithril bars.