how do zircons form - brown zircon crystals - Portugalhow do zircons form - brown zircon crystals - Portugal

How Do Zircons Form?

As a December birthstone, blue zircon is very popular. But are blue zircons natural? Learn how zircons form and get their colors.

8 Minute Read

orangey red zircons - Pakistan
Orangey red zircon crystals on a quartz/biotite mica matrix. Crystals up to about 0.75 cm long. Harchoo, Astore, Northern Areas, Pakistan. © Rob Lavinsky, Used with permission.

Where Do Zircons Form?

Zircons form in many geological environments, including igneous, metamorphic, and sedimentary rocks.

Zirconium Origins

Zircon crystals of igneous origin have an extremely high melting point. They can form within silicic magma as it slowly cools. In this situation, the mineral baddeleyite will melt and provide zirconium (Zr), a necessary ingredient for zircon formation. Under metamorphic conditions, the zirconium in surrounding minerals like baddeleyite can leach out of the mineral and recrystallize into zircon when existing rocks partially melt.

baddeleyite on matrix - South Africa
Jet-black baddeleyite crystal, about 1 cm long, on a gray calcite matrix. Phalaborwa, Ba-Phalaborwa Local Municipality, Mopani District Municipality, Limpopo, South Africa. © Rob Lavinsky, Used with permission.

Zircon Overgrowth

Secondary zircon stones can also recrystallize from liquified primary zircon or form a new outer layer on top of the older zircon crystal in a process termed “overgrowth.” Zircons with multiple layers may or may not show obvious zones.

Metamorphic Zircons

Metamorphic zircon formation can lead to three distinct forms:

  • Bead zircons (tiny individual crystals

Emily Frontiere

Emily Frontiere is a GIA Graduate Gemologist. She is particularly experienced working with estate/antique jewelry.

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