A Small Piece of Blackrock
A Small Piece of Blackrock spawned during various events in the past. Currently, miners occasionally uncover them while Mining. It is also one of the quest items for the quest A Dish Best Served Cold and an ingredient used to make Blackrock Stew from the quest's resulting recipe. You can also penetrate Dark Wisp's psychic barrier by having one inside your backpack.
Even though it was not mentioned in the patch notes of Publish 95 these small piaces now can be stacked (although they must be stacked by type/size).