Question

Background

From the December 29, 2022 NPR article To peer into Earth's deep time, meet a hardy mineral known as the Time Lord:

(Zircons) are really the best markers of Earth's time, or the history of the Earth, says Michael Ackerson, a geologist with the Smithsonian's National Museum of Natural History.)

From the podcast linked on the same page after 01:00:

He tells me that one of the crystals I'm looking at is 4.32 billion years old. Zircons are the oldest known pieces of Earth that still exist on the surface today; the oldest go back as far as 4.37 billion years.

They are the best markers of Earth's time, (for) the history of the Earth.

Ackerson says a zircon crystal originally forms in magma - hot molten rock. Other minerals do too; together they'll make up say, a granite mountain, that slowly weathers away.

Most of the minerals don't survive, they slowly weather away. Quartz, feldspar, they're chemically or physically weathered or eroded, to a point where they're no longer quartz and feldspar. Zircon, and one of the reasons that zircons are so useful, is that zircon is very resilient.

The hearty crystals persist, and eventually get incorporated into another rock as it's forming. That means scientists can crush up the Earth's oldest rocks and pick through the debris, to find little grains of zircon, that are even older.

To know a zircon's age, they zap it with a laser.

Discussion of the use of lasers, argon plasma and detectors to count uranium and lead atoms.

The important atoms are uranium and lead. A growing crystal of zircon loves uranium and will take it in, but zircon hates lead, so if you find lead inside, it pretty surely came from the decay of uranium, which happens at a steady rate, like the ticking of a clock.
Why does zircon hate lead? How do these tiny crystals so effectively exclude lead atoms during formation enabling accurate uranium-lead (U-Pb) dating?

I'm interested in a basic understand of the chemistry that allows a growing crystal of zircon in magma to so effectively prevent uranium from being incorporated while allowing so many other metals in.

Besides uranium and obviously zirconium and silicon, Wikipedia's zircon gives the formula for zirconium silicate as (Zr₁₋_y, REE_y) (SiO₄)₁₋ₓ (OH)₄ₓ₋_y
where REE
stands for rare earth element:

...a set of 17 nearly-indistinguishable lustrous silvery-white soft heavy metals.

The Wikipedia zircon page also says:

Zircon precipitates from silicate melts and has relatively high concentrations of high field strength incompatible elements. For example, hafnium is almost always present in quantities ranging from 1 to 4%.

This seems potentially relevant: Chapter Six - Computer modeling of Zircon (ZrSiO4)—Coffinite (USiO4) solid solutions and lead incorporation: Geological implications

The structure of zircon, ZrSiO4 is modeled using interatomic potentials. The uranium end-member, coffinite (USiO4) and intermediate solid solutions of zircon and coffinite (UxZr1–xSiO4) are then modeled, allowing the prediction of lattice parameters as a function of uranium concentration. Finally, possible structures resulting from the radioactive decay of uranium to lead in coffinite are considered.

Answer 1

Zircon effectively excludes lead atoms during its formation, enabling accurate uranium-lead dating. Zircon incorporates uranium into its crystal lattice but does not readily incorporate lead atoms.

Step-by-step explanation:

Zircon, a zirconium silicate mineral, has the ability to effectively exclude lead atoms during its formation in magma, which allows for accurate uranium-lead (U-Pb) dating. Zircon has a strong affinity for uranium and incorporates it into its crystal lattice.

However, zircon does not readily incorporate lead atoms, as zircon hates lead. As a result, any lead found within zircon crystals is likely from the decay of uranium, which occurs at a steady rate. This makes zircon an excellent mineral for dating purposes.