When in rest a stonejaw looks like a pile of boulders, just like any other. When they rise the boulders form rough arms and legs, and the whole being is some 5 meters tall. The boulders are held together by some magical way. When a stone jaw moves it sounds like someone would grind stone. The voice of a stonejaw is low but has an occasional creak (as if stones were ground together). The age of a stonejaw can be roughly measured by the size and amount of boulders that form its body. More and smaller boulders means an aged stonejaw. It is assumed that an ancient stonejaw would be mostly gravel. A young adult might be as few as 6 boulders.
Stonejaws live together in groups of 2 to 7 individuals. Together they search for rich mineral deposits, which they use for nourishment. Stonejaws are elemental creatures native to the elemental plane of earth. As such they have no natural enemies, but frequently fight with trolls over territories.
Stonejaws are extremely dense creatures. They only think about one thing at a time, and only rarely change their minds. Thus they are virtually immune to mind-effecting spells. They live in small family groups of 2-5 stonejaws. They like to lie and bask in the sun near a cave, which they use as a food mine. Sometimes a ruin on top of a hill might be a stonjaw family taking a nap!
In combat stonejaws try to crush their opponent by smashing into them. They move very fluently and are surprisingly quick in their reactions. Being made of stone, swords do little harm, unless enchanted, so stonejaws are virtually fearless combatants (if they can be bothered to do battle).
If a stonejaw is summoned to the compound plane they only rarely want to leave. Since they have almost no competition here life is simple for a stonejaw, thus they must be forced to leave if the summoner does not want them around (which is generally a good idea). If anyone manages to befriend a stonejaw, this friendship will last for life, since stonejaws have excellent memories, but if one manages to anger a stone jaw....