Zircon Quality Factors

Greenish blue zircon
Zircon’s typical greenish blue colour has been referred to as zircon blue. - Lydia Dyer, gem courtesy of John Dyer & Co.
Zircon is a gemstone that’s not commonly known among jewellery buyers, which is a shame considering the number of beautiful colours it comes in. These include earth tones such as cinnamon, sherry, yellow, orange and red. Among those who are familiar with this gem, zircon is especially admired for its attractive blue colours.

Various zircon colours
Zircon comes in many attractive colours. - GIA & Tino Hammid, courtesy Gordon Bleck
Colour
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.

Zircon ring
Zircon can display earthy colours such as yellow, orange and brown. - Courtesy Richard Krementz Gemstones
12.84-carat triangular-cut zircon
This 12.84-carat triangular-cut zircon displays an attractive orange hue. - John Dyer, Zircon Super Trillion courtesy of John Dyer & Co.
Colourless zircon
One of the most brilliant non-diamond gems, colourless zircon was widely used as a lower-cost diamond alternative in the nineteenth century. 
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.

Intense blue zircon
Intense blue colour in zircon is usually the result of heat treatment. 
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.

Clarity
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.

Emerald-cut blue zircon
Most faceted zircon on the market is free of eye-visible inclusions. - Courtesy Pala International
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.

Cat’s-eye Zircon
Occasionally, long parallel inclusions in zircon will create the cat’s-eye effect when it is cut as a cabochon. - GIA & Tino Hammid, courtesy Gordon Bleck
Cut
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.

Zircon round brilliant
Round-brilliant cut zircons often have an extra set of eight facets at the base of the stone. 
Carat Weight
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.

Zircon round brilliant
Zircon is available in a wide range of sizes, but blue stones as large as this 28.15-carat example are rare.