Titanium in zircon geothermometry
Titanium in zircon geothermometry is a form of a geothermometry technique by which the crystallization temperature of a zircon crystal can be estimated by the amount of titanium atoms which can only be found in the crystal lattice. In zircon crystals, titanium is commonly incorporated, replacing similarly charged zirconium and silicon atoms.
Source: Wikipedia — Titanium in zircon geothermometry (CC BY-SA 4.0)