A lodestone, or loadstone, is a naturally magnetized piece of the mineral magnetite. Ancient people first discovered the property of magnetism in lodestone. Pieces of lodestone, suspended so they could turn, were the first magnetic compasses, and their importance to early navigation is indicated by the name lodestone, which in Middle English means 'course stone' or 'leading stone'. Lodestone is one of only two minerals that is found naturally magnetized; the other, pyrrhotite, is only weakly magnetic. Magnetite is black or brownish-black with a metallic luster, has a Mohs hardness of 5.5-6.5 and a black streak.