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 it was not mentioned in the patch notes of Publish 95 thoose small piaces now can be stacked since this Publish goes live. There are 4 different kind of pieces, so there are 4 different stacks possible.