I have noticed that there is a nice trick of turning these cursed stones to weapon against annoying sieges. Here are the steps to do so:
- Before using the temple and altar reactions turn the temperature off. If you don't do that the cursed stones will vanish immediately. Instead of that we want to save those stone for weapons
- Collect as many cursed stones as you can and want. More is better, as the more stones you have the better chance of severe effects.
- Dump the stone in your entrance. You may want to spread them as much as you can, one stone affects at least all the squares next to it, even wider area. Spreading the stone also increases the chance of more enemies being caught in the gas.
- When the enemy is over the stones turn the temperature back on.
- Witness the poor enemies being caught in poisonous gas!
That's the basic method. I have not tested out the following yet, but I think it should also be possible, with a bit of micromanagement, to use the cursed stones in stone traps. After the traps are and loaded it should be possible to turn the temperature back on without causing the stones to explode. When poor enemy triggers the trap the stone falls over them, exploding immediately and releasing the gas. Just make sure your dwarves are far enough to not be caught in the gas.