They can also damage METAL. It isn't just stone, metal will also get demolished.
Turrets do treat their fireballs like any other explosive and shoot at them.
Some fireballs do make it pass turrets. Fireballs will soak bullets.
Magmasaur is able to destroy ALL STRUCTURES utilizing its searing spit. While it is a walking forge it produces metal at the same rate as a refining forge. You can use the jump button to taunt other creatures and when holding searing spit use crouch to erupt. (This attack pushes creatures back and leaves magma everywhere) it is breedable in lava. Hope this helped