How to remove block of concrete under old toilet
If the floor tile is going underneath it, it should come up pretty easy. do use a chisel and hammer and crack from the top only if possible. You may be able to separate it from the flooring in one piece by setting the chisel at the floor and wedging up the chunk, but you may dislodge tile while you are at it although it will not be likely, still possible. Best to try from the top only, the vibration may make the whole piece come loose anyway....