planet

Zircon

A tiny but nearly indestructible zirconium-silicate mineral, the ideal host for uranium-lead dating. As it crystallizes, zircon locks uranium into its lattice but shuts out lead, guaranteeing a clean starting point. It survives the melting and burial of its parent rock to wash into sandstone - so a single zircon grain can carry billions of years. The oldest known fragment of Earth's crust is a ~4.4-billion-year-old Jack Hills zircon.