The Lump of stone is an item from the skill Dungeoneering. The stone is part of a Dungeoneering puzzle (Magical construct) in which you must repair a giant stone guardian by using a hammer and a chisel to carve the lump of stone into a body part that the guardian is missing which is either his arm, leg, or his head. When you right click on the stone there are four options: Use, Carve, Drop, and Examine. The stone cannot be found in the Grand Exchange though it is tradeable and worth only 1 coin. It can be "sold" to the Smuggler for 0 coins.