Because Pb and Pb are chemically identical, they are usually lost in the same proportions. The term U—Pb dating normally implies the coupled use of both decay schemes in the 'concordia diagram' see below. Both isotopes are the starting points for complex decay series that eventually produce stable isotopes of lead. The amount of radiogenic lead from all these methods must be distinguished from naturally occurring lead, and this is calculated by using the ratio with Pb, which is a stable isotope of the element then, after correcting for original lead, if the mineral has remained in a closed system, the U: However, use of a single decay scheme usually U to Pb leads to the U—Pb isochron dating method, analogous to the rubidium—strontium dating method. Mineralogy[ edit ] Although zircon ZrSiO4 is most commonly used, other minerals such as monazite see: Uranium-lead dating was applied initially to uranium minerals, e.