Zirconium in Zircon

only cerium is a ree, and it only occurs in zircon in lab experiments at doping.

You want yttrium , lutetium or samarium. We have a condition in lanthanides called shrinking of the ions so cerium usually occurs in "Defect lattices " of thinks like phosphapte rocks and the sort.
We use Titanium as a zircon clock because it only occurs in the defect as a function of PT