If you check in your diary (or if you press "a" for your automap, you will notice tabs at the right hand side of the screen. One of which is trophies.
If you look in there, you will see what damages the stone gargoyles do (provided you have killed at least one). You can then use the crystals to your benefit, but making yourself a little more "immune" to the type of damage they do.
You should also be able to see what they are vulnerable to. (IIRC spiritual damage kills then the easiest, so find a weapon that does some spiritual damage.