Minerals that are magnetic usually contain oxides of iron, and the best example of a magnetic mineral is lodestone which is also called magnetite. It has the formula Fe₃O4 (just like water has the formula H₂O, Fe is iron and O is oxygen. Atoms have electrons, protons, and neutrons (with protons and neutrons in the nucleus) and it is the electrons in certain atoms that give rise to magnetic behavior. Electrons are associated with a property called spin -- each electron in effect is a little magnet with a north pole and a south pole. When the number of electrons in atoms is arranged in certain special way (as they are for iron atoms) the spins add up to make the whole atom magnetic.