Fourth, zircon is physically tough and easily separated from crushed rock samples because of its high density.Other minerals sometimes used for uranium-lead dating include monazite, titanite and two other zirconium minerals, baddeleyite and zirconolite.Uranium easily substitutes for zirconium while lead is strongly excluded.
Third, zircon is widespread in igneous rocks as a primary mineral.
This makes it especially valuable for dating these rocks, which have no fossils to indicate their age.
The favorite mineral among U-Pb daters is zircon (Zr Si O), for several good reasons.
First, its chemical structure likes uranium and hates lead.
Some zircons are obviously disturbed and can be ignored, while other cases are harder to judge.
In these cases, the concordia diagram is a valuable tool.
Uranium dating is one of the ways of determining the age of ancient objects, even one million years old, by measuring how much of the following are present in them: the amount of radioactive isotopes of uranium, and the amount of other materials into which the radioactive isotopes would decompose.
These measurements, when combined with knowledge about the initial state of matter under study (that is, composition at the time of death of an organism, or formation of a mineral) and the rate at which radioactivity takes place, would yield the age of the object.
Lead atoms created by uranium decay are trapped in the crystal and build up in concentration with time.