The Stone Key is a blue diamond-shaped key that appears early in Golden Sun: Dark Dawn. It is found in an room in the upper levels of the Konpa Ruins, the same room the Grip Crystal appears in, and is used to exit the room.
Once a player acquires the Grip Crystal, the room will transform and a message will appear telling the player that they must demonstrate the Grip Psynergy to leave the room. In this way, the Stone Key helps to demonstrate the use of Grip to a player. To reach the Stone Key, the player must grip the grip-able right column then use grip to "catch" the Stone Key. Grip the left grip-able column then head over to the door. Place the Stone Key into the diamond-shaped hole then exit the room.