Can't find this anywhere:
"door stones" are descripted as "consumable, opening any visible door" but whan i try to use it with any character near the locked doorm it tells "no valid target found" or somethig like this. And the door stays closed until i craft the key.

What is the purpose of the item and how do I use it properly?

I think it only work with Wood Door (the door that doesn't need key but only Skill Unlock)

Well, then, it seems a pretty useless item, considering some units have lockpick.
Thanks for your help.