Lodestone is a naturally occurring magnetic material, made of iron and oxide. The magnetism is caused by the material having formed in the Earth's magnetic field.

It was known to the ancient Greeks, but the word 'magnet' is derived from Magnesia, in China, where lodestone was common. The Chinese first used it to make divining boards, but were soon using it to make compasses used in navigation and possibly also in astrology and astronomy. They discovered that iron could be made into magnets with the aid of lodestone and made the first magnets out of little iron needles. With the aid of these compasses they could explore the entire pacific basin.

It took much longer – maybe a thousand years - for compasses to to be made in the west. It took a further four hundred or so years for investigation into magnetism before experiments William Gilbert conducted in the sixteenth century with lodestone, magnets and electrical materials to show this. show that the Earth behaved like a giant magnet.