A radiometric dating method based on the fact that background radiation causes electrons to separate from their atoms and become trapped in the crystal lattice of minerals. When odd numbers of electrons are separated, there is a measurable change in the magnetic field (or spin) of the atoms. Since the magnetic field progressively changes with time in a predictable way as a result of this process, it provides an atomic clock, or calendar, that can be used for dating purposes. This technique is employed primarily to chronometrically date calcium carbonate in limestone, coral, teeth, mollusks, and egg shells. It can also date quartz and flint.