Heat up a rock. Most likely, all you will get is a hot rock. But
heat up the right type of stone to just the right temperature
and you could end up with a magnet, scientists now report. Long
before people invented the small magnets that stick to
refrigerators or the big magnets that pick up cars at the
junkyard, people discovered natural magnets. The most magnetic
and common type is a lodestone. It consists of a brownish-black
mineral called magnetite. Lodestones are natural compasses:
Suspend one by a thread or wire and it will rotate until its
magnetic field is aligned with Earth’s magnetic field. A
magnetic field is the area around a material in which its
magnetic forces can be detected. Those forces stem from the
activity of tiny, negatively charged particles called electrons,
which are within all atoms. A material’s magnetism is determined
by the way its electrons move around the outside of its atoms’
nuclei — particularly those electrons that aren’t paired with
other electrons in certain ways. If a larg