Lodestone (also spelled loadstone) is a special type of the mineral magnetite. All varieties of magnetite display signs of magnetism, but of them, only lodestone possesses distinctly north-south polarity. Lodestone and other magnetic iron ores often occur in igneous and metamorphic rocks found around the world.
Because it occurs naturally, lodestone has been known for thousands of years. Even the ancients observed that lodestone attracts iron. They pondered this mysterious behavior in their philosophical discussions and writings. The oldest known reference to lodestone’s properties appeared in 600 BC, when the Greek philosopher Thales of Miletus noted iron’s attraction to it. Thales attempted to explain the phenomenon through animism, presuming that the lodestone possessed a soul. Other philosophers developed their own theories, but to most ancient people the lodestone was an unexplainable mystery.
Just because they didn’t know how lodestone worked, doesn’t mean that early humans did not find uses for it. In China, lodestone appeared in divining boards used by fortune tellers to predict the future. The lodestone also served as the basis of primitive Chinese compasses that could roughly indicate the cardinal directions. At first these compasses chiefly served as a tool to help the Chinese harmonize their lives in the ways outlined by their ancient philosophical teachings. But improved compasses eventually helped guide many great explorers to new, exciting places around the globe. Today lodestone is more commonly found in classrooms, where teachers use it to help demonstrate the basic principles of magnetism.
Despite the modern understanding of magnetism, the shroud of mystery surrounding lodestone for so long has never been completely eliminated. In recent years, scientists have questioned exactly why lodestone is relatively rare compared to other kinds of magnetite. Dr. Peter Wasilewski of NASA's Goddard Space Flight Center recently demonstrated that only magnetite with a specific composition and crystal structure has the potential to become lodestone. The pieces of magnetite that naturally realized this potential, Wasilewski believes, did so by being struck with lightning. The electric discharge that accompanies lightning creates a temporary, but very strong magnetic field. This field, Wasilewski argues, is strong enough to magnetize lodestone, while the earth’s magnetic field is not. Wasilewski has successfully demonstrated the magnetization of pieces of magnetite at a laboratory in New Mexico that specializes in lightning studies, providing strong support for his theory.