However, it is possible to put a date on some sedimentary rocks using the mineral xenotime (YPO).
Uranium can and often does substitute for the element yttrium, whereas lead cannot, making xenotime suitable for radiometric dating.
The reader will find this article much easier to grasp if s/he has already mastered the material in the articles on K-Ar dating, Ar-Ar dating, and Rb-Sr dating.
Pb (lead-204), which is neither unstable nor radiogenic.
Unlike the ordinary isochron methods such as Rb-Sr, the Pb-Pb method does not allow us to deduce the original proportions of the various lead isotopes from the data acquired from the sample. We can do this by finding minerals that contain lead but never contained any uranium, or only ever contained it in negligible quantities.
Troilite (Fe S) from iron-rich meteorites fits the bill: its present ratio of uranium to lead is so tiny that either the solar system and indeed the universe is many many times older than cosmologists think, or, given the long half-life (4.5 billion years) of U, there can hardly have been any uranium in the meteorites to start with, and so its decay can hardly have affected the lead isotope ratios of these meteorites.
Zircons, then, are relatively immune to the problems that make isochron U-Pb dating so difficult.
But of course for isochron dating we need more than one mineral; zircons alone would not be enough.As a result, we expect speleothems when they are first formed to contain some uranium but little or no lead — just like zircons.So we can apply the same technique to speleothems as we do to zircons.We report here on reconnaissance studies of fission track dating of zeolites, a complex group of tectosilicates, which is, for example, widely developed in basaltic rocks after their emplacement by later stage processes.In this article we shall discuss the basis of the U-Pb and Pb-Pb methods, and also fission track dating.So by dating the xenotime crust, we can find out when the zircon it's growing on became sediment; dating the zircon itself would tell you the age of the parent rock.