A rock, on the other hand, may contain minerals formed at more than one time under a variety of conditions.Under such circumstances the isolation and analysis of certain minerals can indicate at what time these conditions prevailed.Here, a single uranium–lead isotopic analysis can provide an age more precise than can be obtained by the whole rock isochron method involving many analyses.
Other model ages can be calculated using neodymium isotopes by extrapolating present values back to a proposed mantle-evolution line.
In both cases, approximate ages that have a degree of validity with respect to one another result, but they are progressively less reliable as the assumptions on which the model is calculated are violated.
In some cases the discovery of a rare trace mineral results in a major breakthrough as it allows precise ages to be determined in formerly undatable units.
For example, the mineral those composed primarily of one or more ferromagnesian, dark-coloured minerals).
In this case, it is a big advantage to present the data in a form in which the abundance of both the parent and daughter isotopes are given with respect to the abundance of the initial background daughter.