Zircon is a colorful gem with high refraction and fire that’s unfairly confused with cubic zirconia.
Zircon occurs in an array of colors. Its wide and varied palette of yellow, green, red, reddish brown, and blue hues makes it a favorite among collectors as well as informed consumers.
Zircon crystals grow in many different types of rock and possess a range of optical and physical properties.
Some zircons—usually green ones—display much lower values for these properties than others. Scientists have determined that the crystal structures of these gems were almost completely broken down by radioactive elements—often present in zircon as impurities—that damaged the gems’ crystal structure over long periods of geological time.
Some gemologists classify zircons into three types—high, intermediate, and low. A zircon’s classification depends on its properties, which are directly related to the amount of radiation-induced damage done to its crystal structure.
- Mineral: Zircon
- Chemistry: ZrSiO4
- Color: Blue, red, yellow, orange, brown, green
- Refractive index:
- High: 1.925 to 1.984 (+/- 0.040)
- Medium: 1.875 to 1.905 (+/- 0.030)
- Low: 1.810 to 1.815 (+/-0.030)
- Birefringence: 0.000 to 0.059 (low to high)
- Specific gravity: 3.90 to 4.73
- Mohs Hardness: 6 to 7.5 (low to high)
Birthstones and Anniversaries
Zircon is a birthstone for the month of December, along with turquoise and tanzanite.
Zircon Gemstone as rough
High or normal zircons have full crystal structures, with little or no damage from radioactive elements. As a result, they have the normal physical and optical properties associated with the mineral.
In intermediate or medium zircons, radioactive elements have caused some structural damage. They have physical and optical properties that are between high and low types.
Extensive crystal-structure damage from radioactive elements results in low zircons with much lower optical and physical properties. In extreme cases, they are practically amorphous, which means they lack an orderly crystal structure.
Virtually all the zircons used in jewelry are of the high type. Interestingly, radiation-induced crystal-structure breakdown can be reversed somewhat by heating zircon to high temperatures. High-temperature heat treatment repairs the stone’s damaged crystal structure.
Zircon History and Lore
Many people have heard of zircon but never seen it. This is mostly because of colorless zircon’s wide use as a diamond simulant in the early 1900s. It was long ago replaced in that role by more convincing look-alikes, but its name still means “imitation” to many people. That’s unfortunate because zircon is a beautiful colored stone with its own fair share of folklore and charm.
In the Middle Ages, this gem was thought to induce sound sleep, drive away evil spirits, and promote riches, honor, and wisdom.
Many scholars think the stone’s name comes from the Arabic word zarkun, meaning “cinnabar” or “vermilion.” Others believe the source is the Persian word zargun, or “gold colored.” Considering zircon’s color range, either derivation seems possible.
Blue zircon was a particular favorite in Victorian times, when fine gems were often featured in English estate jewelry dating from the 1880s. Gemologist George Kunz—Tiffany’s famed gem buyer—was a notable zircon advocate. He once proposed the name “starlite” to promote the gem’s fiery nature. The name never caught on.
Facts about Zircon Gemstone
With radioactive trace elements that tick off time, zircon is a geological clock that tells us about the early earth.
Zircon has very high luster, refractive indices, and dispersion, giving it lots of brilliance and rainbow flashes of fire.
Zircon’s pronounced double refraction means you can see twice as many facets and twice as much fire.
The most valuable colors of zircon are blue, bright red, and green.
Zircon is often eye-clean. Gems with noticeable inclusions are less valuable.
To maximize its brilliance, zircon is most often cut in rounds and ovals.
Zircon in fine quality is rare in large sizes. Zircon weighs more than most gems of like size.