method of age determination that makes use of the damage to crystals and the radiation from radioactive substances caused by storage of energy in electron traps. In the mineral zircon, for example, radiation damage results in a change in colour, the storage of energy in electron traps, and a change in the crystallographic constants of the mineral. Extensive damage may result in a metamict mineral (that is, a mineral in which the crystal structure has been destroyed); the change in crystallographic constants is a function of the total radiation damage, which depends on the amount of radioactive substances and the age of the mineral. Thus, measurement of uranium and thorium content in the zircon, combined with measurement of its crystallographic constants, provides a measure of its age. Compare fission-track dating. (fission-track dating)