But we can infer from the interactions we have had with the Doctor and the Angels that they might simply be tougher than they would appear even if they look to be made of stone or a stone-like material.
Are the the product of selective breeding? Though this took time and effort and they only came close to breaking through the warding before they were killed.
It was also shown that the blades can kill in , and that they could kill in.
However, there are many means that can be used against angelic beings.