Zircon growth rings.
Zircons usually occur as rare and tiny minerals in the rock. They grow slowly as the magma in the Earth’s crust cools down. This slow growing process is captured here by the concentric rings just like in the tree, however the age order of these rings is reversed in this case (center crystallizes first and outer ring last).
What you are looking at is a single zircon grain that is about 0.01 mm across. This grain has been cut in half to reveal it’s inner structure by an imaging method called cathodoluminescence.