Zircon Quality Factors
Some zircons display warm autumnal earth tones such as yellowish and reddish brown, inspiring fashion trends. Red and green zircons have market value as collectors’ stones, and cat’s-eye zircons occasionally appear on the market. There are also colourless zircons.
Although collectors clearly love zircon’s colour variety, consumers seem most enamoured of just one hue: blue. Gem dealer reports indicate that at least 80 percent of zircons sold are blue.
Because they’re in greater demand, blue zircons usually command higher prices than any of the other varieties. Even though gem buyers can satisfy their demand for blue gems with top-grade topaz at significantly lower cost, blue zircon continues to sell well. Industry analysts believe that blue zircon has yet to reach its full market potential.
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.
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 jewellery.
Today, most zircon that is faceted for use in jewellery is free of inclusions that are visible to the eye. Eye-visible inclusions cause a drop in zircon value.
Rarely, zircon might contain long parallel inclusions that create the cat’s-eye effect when the stone is cut as a cabochon.
It’s a challenge to cut zircon because the gem is 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 gem’s lower portion, called the pavilion. This isn’t seen very often today because of the extra labour costs involved. Zircon can also be found in step cuts, which have rows of parallel facets, and mixed cuts, which are a combination of brilliant and step-cut facets.
The supply of zircon is generally limited, and typical sizes depend on colour. Blue or green stones normally range from 1 carat to 10 carats and yellows and oranges up to around 5 carats. Reds and purples are usually smaller.