Lodestone is naturally occurring magnetite that has already been magnetized, most likely by a lightning strike, before anyone finds it, which made it a genuine curiosity in every culture that encountered it: a stone that visibly and repeatably attracts iron with no human intervention required. Chinese sources from as early as the Han dynasty describe lodestone's directional property, and by the eleventh century Chinese texts describe magnetized needles used for navigation, a practical application that spread west and underlies the maritime compass still in use today.
The property was well enough known in the ancient Mediterranean that "magnet" itself likely derives from Magnesia, a region of Asia Minor associated with the stone in Greek accounts, though which specific deposit the name refers to is not fully settled among historians of the term.
The eleventh century text usually credited with the earliest clear account is Shen Kuo's Dream Pool Essays, which describes magnetising a needle by rubbing it on a lodestone and suspending it so that it can turn freely, and which also notes that the needle does not point exactly south, an observation of magnetic declination made centuries before the effect was recorded in Europe.
Lodestone's behaviour made it a natural subject for early natural philosophy in the West as well. William Gilbert's De Magnete of 1600 worked outward from lodestone experiments to the conclusion that the earth is itself a great magnet, which is the point at which the stone stops being a marvel and becomes a piece of physics.