The broken pickaxe was the remains of a pickaxe after a player attempted to extract ore from a smoking rock and the rock exploded. Nurmof repaired broken pickaxes for free or a fee depending on the pickaxe type. It was not possible to mine with a broken pickaxe. It was only possible to sell undamaged pickaxes to Nurmof's Pickaxe Shop in the Dwarven Mines but you could sell broken pickaxes to any player. You could also buy or sell the heads and pickaxe handles from other players. Bob at his axe store in Lumbridge could repair broken pickaxe for a price depending on the type.