Uranium-lead dating is one of several radiometric dating techniques. It is the oldest method and generally considered to be the most accurate. It dates a material based on the half-lives for the decay of U238 to Pb206 or of U235 to Pb207. 
This dating method is used on several minerals, however, it works best with the mineral zircon (ZrSiO4). Because the formation of zircon rejects lead from its structure but allows uranium in the place of zirconium atoms, the formation of the crystal is given a reliable date. Zircon is also preferred for it high toughness and ease of separation from other rocks.