Zircons from Jack Hills in the Narryer Gneiss Terrane, Yilgarn Craton, Western Australia, have yielded U-Pb ages up to 4.404 billion years, interpreted to be the age of crystallization, making them the oldest minerals so far dated on Earth.
In addition, the oxygen isotopic compositions of some of these zircons have been interpreted to indicate that more than 4.4 billion years ago there was already water on the surface of the Earth.
Zircon is also very resistant to heat and corrosion.
Because of their uranium and thorium content, some zircons undergo metamictization.
Zircon forms in silicate melts with large proportions of high field strength incompatible elements.
Due to its hardness, durability and chemical inertness, zircon persists in sedimentary deposits and is a common constituent of most sands.
Currently, zircons are typically dated by uranium-lead (U-Pb), fission-track, cathodoluminescence, and U Th/He techniques.
For instance, imaging the cathodoluminescence emission from fast electrons can be used as a prescreening tool for high-resolution secondary-ion-mass spectrometry (SIMS) to image the zonation pattern and identify regions of interest for isotope analysis.
When ‘parent’ uranium-238 decays, for example, it produces subatomic particles, energy and ‘daughter’ lead-206.
Isotopes are important to geologists because each radioactive element decays at a constant rate, which is unique to that element.