The correct answer is lodestone. Lodestone is a naturally magnetized piece of magnetite. It is a black mineral that is found in many parts of the world. Lodestones were used by early sailors as a primitive compass because they would align themselves with the Earth's magnetic field. This allowed sailors to determine the direction of north and south, which was essential for navigation. Lodestones were also used in the development of the first compasses, which were invented in China during the 11th century.