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Zircon

Zircon’s popularity has been increased by widespread exposure on home-shopping television networks. As an affordable stones like zircon falls neatly into the price range of many home-shopping buyers. Besides that, warm hues such as yellowish and reddish brown have tapped into fashion trends for autumnal russet and earth colors.

Exotic red and green zircons also have market value as collectors’ stones. Cat’s-eye zircons occasionally come on the market as curios.

Recent reports from dealers indicate that at least 80 percent of zircons sold are blue. Blue zircons usually command higher prices than any of the other varieties because they’re in greater demand. Even though the cost of top-grade topaz is significantly lower, blue zircon continues to sell well. Industry analysts believe that blue zircon has yet to reach its full market potential.

ZIRCON COLOR

Other than colorless zircon that was widely used as a lower-cost diamond alternative in the nineteenth century, zircon occurs in a rainbow of colors to rival both tourmaline and sapphire. Its wide and varied palette of yellow, green, red, reddish brown and blue hues makes it a favorite among collectors and informed consumers alike. Zircon crystals grow in a wide variety of different rock types. They’re common in both igneous and metamorphic rocks.

BLUE ZIRCON

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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.

Zircons are relatively free of inclusions. But many untreated zircons have a cloudy or smoky appearance. If it’s extreme, it can be a negative factor with buyers. In Victorian times, this smokiness made zircon a popular gem for mourning jewelry.

Zircon’s blue, almost always the result of heat treatment, comes in a range that includes very slightly greenish blue, greenish blue, and very strongly greenish blue. While blue remains the dominant color, a range of options awaits designers and consumers. Besides colorless, other zircon colors are red, yellow, orange, brown, and green.

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Cutting zircon is a challenge because it’s brittle. Cutters usually fashion zircon in the brilliant style to take advantage of its luster and fire. A modification of the brilliant cut, known as the “zircon cut,” uses eight extra facets around the base of the pavilion. This isn’t seen very often today because of the extra labor costs involved.

Zircon can also be found in step cuts and mixed cuts. Dealers report that step cuts are popular with buyers.

ZIRCON CRYSTAL STRUCTURE

Over long periods of geological time, emanations from radioactive impurities—either uranium or thorium—damage zircon’s crystal structure. In extreme cases, the crystal structure has almost completely broken down and the stones are practically amorphous.

There are three types—high, intermediate, and low—depending on properties, which are directly related to the degree of radiation-induced damage to their crystal structure.

    1. High or normal zircons have fully crystalline structures, with little or no damage from radioactive elements. Virtually all the zircons used in jewelry are of the high, fully crystalline type. High zircons have the normal physical and optical properties associated with the mineral.
    2. Intermediate or medium zircons have physical and optical properties that are between high and low types. Radioactive elements have caused some damage to their crystal structures.
    3. Low zircons (metamict) have had extensive damage to their crystal structures from radioactive elements. Low zircons have much lower specific gravity, refractive index, and double refraction than other types.

Interestingly, the metamict process is reversed if zircon is heated to high temperatures. Heating repairs the stone’s damaged crystal structure and restores some metamict zircon to its fully crystalline form. Specific gravity, double refraction and refractive index values might all return to normal.

ZIRCON SOURCES AND MARKETS

Zircon sources in Southeast Asia—and recently discovered deposits in Madagascar—easily meet demand. Prospectors often find zircon when they’re actually looking for blue sapphire. Zircon sources that overlap with sapphire sources include Sri Lanka, Myanmar, Vietnam, and Cambodia.

Cambodia is the primary source for blue zircon and heat-treatable zircon. Most of its rough is treated and then sold to cutters in neighboring countryThailand.

ZIRCON TREATMENTS

In nature, most zircons are yellowish or reddish brown. Natural colorless, blue, and red zircons are rare. Gem dealers have been heat-treating zircon for centuries. It began when they found that they could turn cinnamon-colored zircons to more brilliant, colorless zircons by heating them. They sold them as Matura diamonds, named after the place in Sri Lanka where the original colored zircon was found.

The color of heat-treated blue zircon is usually stable and undetectable. Although buyers should be told if the color they’re buying is the result of treatment and could fade over time, heat-treated gems have a good reputation for permanently holding their color.

    1. Treaters surround the gems in charcoal and heat them to about 1600°F (875°C). After a few hours, some zircons become colorless, some blue, and some remain brown or yellowish.
    2. Treaters might then subject the brownish stones to a second round of heating in charcoal.
    3. Any remaining gems that don’t turn blue or colorless might then be heated in air at 1450°F (800°C). Many of these stones become colorless, strong yellow, orange, or red.
    4. Gems that don’t respond to treatment might be heated a number of times.

Most dealers assume that a colorless, blue, or red zircon is treated because these colors are very rare in nature. But buyers should be told that these colors result from heat treatment and can fade over time. Fortunately, heat-treated gems have a good reputation for holding their color permanently, and the color of heat-treated blue zircon is usually stable and undetectable.

ZIRCON CARE AND HANDLING

Zircon is relatively soft at 7 to 7.5 on the Mohs scale. However, zircon can be brittle—especially heat treatment can make it even more brittle. Careless handling can abrade crisp facet edges. Loose zircon should be packed in individual stone papers for protection.

In finished jewelry, zircon should be set so its edges are protected. It should be used in jewelry where it receives minimal abuse—brooches, pendants, earrings, and pins are good choices.