Where to begin with this one .... plants weigh one stone, plant clippings also weigh one stone ; a plant weighs one stone but can have 16 stones of seeds and resources on it, which weigh nothing until you take them off the plant ; small pieces of gargoyle stone armour weigh less than a huge stone table ; a stone chair is also far lighter than almost every weapon, human elf or gargoyle, in the game, half the weight of a cleaver ....
The list of non-intuitive or completely illogical 'weights' in the game is almost endless