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Material World
Mineral · ZrSiO4

Zircon

A tough silicate that traps uranium and refuses lead — which is how the age of the Earth is known, and the only real source of zirconium.

Ore Gemstone Refractory

Zircon's importance rests on a quirk of its chemistry. When it crystallises it accepts uranium into the site zirconium would occupy, and rejects lead almost completely. So any lead found inside a zircon crystal arrived there by the decay of uranium after the crystal formed, and the ratio between them is a clock that started when the mineral did.

Zircon is also extraordinarily durable — hard, chemically resistant, and surviving erosion, transport and burial intact. Grains have been dated to more than four billion years, older than any surviving rock, and they are the principal physical evidence for what the early Earth was like.

How to identify it

Zircon is hard, heavy and brilliant, with an adamantine lustre and strong dispersion that made it the traditional diamond substitute before synthetic stones. Crystals are stubby tetragonal prisms with pyramidal ends.

Some specimens are partly metamict — their structure damaged by the radiation of their own uranium — which lowers the hardness and density and makes the mineral cloudy.

Uses

Most zircon is used as sand rather than as a metal source: in foundry moulds, refractory linings and ceramic glazes, where its heat resistance and low thermal expansion matter.

It is also the ore of zirconium and, inseparably, of hafnium — the two are chemically so alike that separating them is among the more difficult operations in industrial chemistry, and the separation matters because zirconium is nearly transparent to neutrons and hafnium absorbs them, which makes one a reactor cladding and the other a control rod.

Medium confidence Weak evidence

How we know: checked recently · only one source, so there is nothing to cross-check it against · stated directly by the source.

How this connects

Where a connection has been confirmed by an outside reference, that reference is named beside it.

is an ore of

  • Zirconium — element · the only significant source, and of hafnium with it Wikidata
  • Hafnium — element · inseparable from zirconium until a notoriously difficult chemical separation

is an alternative to

  • Diamond — mineral · as a gemstone only: zircon's dispersion and adamantine lustre made it the traditional diamond substitute, long before synthetic stones. It is nowhere near as hard

is commonly confused with

  • Xenotime — mineral · both tetragonal phosphate-like prisms in the same heavy mineral sands; zircon is harder and denser

is a component of

  • Gneiss — rock · the accessory that dates the rock — zircon survives metamorphism and holds the uranium-lead clock that gives shield gneisses their ages
  • Granite — rock · the classic granite accessory — a fraction of a per cent by mass, and the mineral nearly every date for a granite is measured on

is a source for

  • Hafnium — element · always with zirconium in zircon, from which it is separated only because reactor-grade zirconium must be free of it — hafnium absorbs the neutrons zirconium lets through

contains

Sources

  • Material World
    Our own writing
  • Wikidata
    Wikimedia Foundation · Creative Commons CC0 1.0 Universal (public domain dedication)
  • Crystallography Open Database
    COD Advisory Board / Vilnius University · CC0 — contributors place data in the public domain

Questions this page answers

Where it comes from, and what it becomes

Follow Zircon back to what it starts as, and forward into what it becomes. Each step is a documented one — a real route material takes, not a chain of inference.

Downstream — what it becomes

  • Zircon → is an ore of (inseparable from zirconium until a notoriously difficult chemical separation) → Hafnium → is a component of (a fraction of a per cent, at the grain boundaries of the alloys that still have grain boundaries) → Nickel superalloy → is used in (cast as a single crystal, because at temperature and sustained load the failure mode is creep along grain boundaries — so the boundaries are removed entirely) → Turbine blade → is associated with (the jet engine created the superalloy industry, because no existing material survived the turbine inlet — and turbine temperature has risen about 500 °C since, almost entirely on the blade) → The wartime materials programmes complete chain
  • Zircon → is a component of (the classic granite accessory — a fraction of a per cent by mass, and the mineral nearly every date for a granite is measured on) → Granite → is a source for (quarried in blocks for cladding, kerbs and monuments) → Dimension stone → is used in (quarried rather than mined, and the distinction is legal and technical rather than merely a word) → Mining and quarrying → is associated with (steam pumping allowed mines below the water table, which is what made deep coal possible) → Industrial Revolution complete chain
  • Zircon → is an ore of (the only significant source, and of hafnium with it) → Zirconium → is used as (fuel cladding, chosen because it lets neutrons through) → Nuclear fuel
  • Zircon → is a component of (the accessory that dates the rock — zircon survives metamorphism and holds the uranium-lead clock that gives shield gneisses their ages) → Gneiss
  • Zircon → is a component of (the classic granite accessory — a fraction of a per cent by mass, and the mineral nearly every date for a granite is measured on) → Granite → is an input to (cut with diamond wire for dimension stone, and crushed elsewhere for aggregate) → Quarrying → produces (cut rather than blasted, because a quarry that shatters its stone has destroyed what it came for) → Dimension stone → is used in (cladding, flooring, kerbs and monuments) → Construction
  • Zircon → is an ore of (inseparable from zirconium until a notoriously difficult chemical separation) → Hafnium → is used in (in the directionally solidified grades that still have grain boundaries, to strengthen them) → Turbine blade → is used in (and the capability is the casting yield and the coating rather than the alloy, whose composition is published — which is why jet engines are a three-company industry) → Aerospace manufacture

These are the most distinct paths onward. Zircon ends up in others besides.