A lodestone is a piece of the mineral magnetite – a highly magnetized substance – that when suspended orientates itself with the direction and polarity of Earth’s magnetic field. Due to this innate ability, lodestones were used as the world’s first compasses, with their current name derived from the Middle English term for ‘leading stone’.
Not all magnetite is naturally magnetized however, with only a small amount of the mineral – which is largely found in Earth’s crust – able to be used as a lodestone. Indeed, research suggests that only strains of magnetite with a specific crystalline structure has the necessary coercivity (resistance to being demagnetised) to be utilized as a navigational aid.
NASA scientist Dr Peter Wasilewski believes lodestones are created by the introduction of lightning discharges to magnetite. While short-lived a lightning bolt could create a very strong magnetic field capable of magnetising the mineral.