Stone dragons have a tough outer covering made of a stone-like material. They eat rocks, using the minerals they contain for nourishment and to keep up their stone outer shell. They rarely move, and are the heaviest of all types of dragons. Although they have wings, indicating flight ability, no one has ever seen a stone dragon flying.
Aquarium spends her time on a battlement looming over a particularly wide strip of moat, glaring down at the little fish swimming around. Why, you might ask. While it has been thought that she just liked the taste of sushi (sans seaweed, rice, and everything else), it's been discovered that she actually thinks of the little creatures as her children, and raises the fish to be beautiful. This attracts a lot of unwelcome attention from the other Dragons, who don't understand her taste in beauty, but any argument is met with a stony stare (pardon the pun) and a tail-lash.