Zircon has a very high melting point, is fairly hard (Mohs hardness 6.57.5), and is resistant to weathering. As a result, zircon grains can remain unchanged after being eroded from their mother granites, incorporated into sedimentary rocks, and even metamorphosed. That makes zircon valuable as a mineral fossil. At the same time, zircon contains traces of uranium suitable for age dating by the uranium-lead method. Zircon is the gold standard for dating ancient granites, which can be hard to date with other methods.
Learn more about zircon and other zirconium minerals.