Lodestone is one of only two minerals that is found naturally magnetised; the other, pyrrhotite, is only weakly magnetic. The property of magnetism was first discovered in Antiquity through lodestones, and pieces suspended so that they could turn were the first magnetic compasses. This discovery was of immense importance for early navigation, although for a couple of millennia at least, notably among the Olmecs and Han Chinese, lodestones were used exclusively for geomancy. In Middle English ‘lodestone’ meant ‘leading stone’, and ‘lode’ once meant ‘journey’. The process by which lodestone is created has long been an open question in geology, and only a small amount of magnetite on earth is found magnetised as lodestone.