February 2012 Newsletter: Natural Zircon Gems

Zircon, like spinel, is one of those gemstones which is highly regarded by gem dealers and collectors, but is not well known in the commercial jewelry market. Indeed, many consumers are liable to confuse natural zircon with cubic zirconia, a cheap synthetic diamond simulant.

Natural zircon is actually one of the more fascinating gemstones in the world, with a number of interesting properties. Zircon is noted especially for its high refractive index and excellent fire. In fact zircon has a higher refractive index than sapphire, ruby, spinel or tanzanite. Zircon also has very impressive fire, with a dispersion rating nearly as high as diamond. Found in a range of colors, including blue, red, pink, orange, honey, green and white, zircon makes very attractive jewelry indeed.

In addition to its obvious beauty, zircon has some unusual properties. For example, it has very pronounced birefringence or double refractivity, where the difference between the two refractive indices is unusually high. This can often be observed with the naked eye when you look down through the table of a cut zircon: you will observe facet doubling that makes the facet edges looked blurred. Zircon is also a remarkably dense mineral, with a density about 50% higher than diamond. Only a few minerals such as hematite and cassiterite have a higher density.

The rare green zircon is especially unusual. It results from a process known as metamictization, where traces of radioactive uranium and thorium disrupt the crystal structure. Eventually the material becomes an isotropic glass. These green zircons still maintain the distinctive zircon fire, however, and they are prized by collectors.

Gemologically, zircon is a zirconium silicate by chemical composition, with a hardness of 7.5 on the Mohs scale. It is suitable for all kinds of jewelry, though protective settings are recommended for rings. 

The traditional sources for zircon are Sri Lanka, Burma and Cambodia. These days most of the fine blue zircon comes from Cambodia. But Tanzania has become an important new source for red, orange and honey zircon. Blue zircon is produced by low temperature heating, but only the Cambodian and Burmese zircon will turn blue when heated.

Compared to sapphire or spinel, zircon is very affordable, and high quality specimens can be found in larger sizes as well. Since zircon is such a dense material, it is always a good idea to check the size as well as the carat weight when buying zircon.


Notable Gems from the AJS Collection

This month we feature some of the finest zircons from our collection.


13.79 ct. Blue Zircon from Cambodia  [SOLD]

The top color for blue zircon is a pure saturated blue with a medium to medium dark tone. This large zircon pear combines top color with outstanding clarity -- we've given it our highest clarity grade ("loupe clean"). Beautifully cut to maxmize its brilliance, this gem has amazing sparkle. With a size of 15 x 10 mm, this fine zircon will make a superb pendant. See all our blue zircon.


23.86 ct Honey Zircon from Burma  [SOLD]

This huge zircon from Burma displays an unusual mix of yellow, green and brown earth tones. Precision cut in a symmetrical cushion, this very clean material shows the brilliance and fire that has made zircon a favorite among gem connoisseurs. Completely natural and untreated, a zircon in this size is a real collector's item. See all our honey zircon.


6.79 ct Red Zircon from Tanzania  [SOLD]

Blue and red have tended to be the most valuable colors in natural zircon. Pure red is hard to find, but this fine specimen from Tanzania displays a deep ruby red with no trace of brown. The combination of large size, excellent clarity and top color make this an exceptional gem. See all our red zircon.


7.01 ct White Zircon from Tanzania  [SOLD]

In the days before synthetic diamond simulants like CZ and moissanite, white zircon was the preferred subsitute for diamond, since no other natural gemstone can appromixate diamond's brilliance and fire. White zircons are still popular, especially in larger sizes. This completely clean 7 carat white zircon from Tanzania is a good example. White zircon is generally heated at low termperatures to remove any traces of color. See all our white zircon.


7.76 ct Blue Zircon from Cambodia  [SOLD]

Deep blue zircons are quite rare. A light to medium blue is more typical, usually with a slight greenish secondary hue. This 7.76 ct Cambodian zircon is a good example of the medium blue. Very clean and fashioned in a portguese cut to maximize brilliance, this 12 x 10 mm gem is suitable for either a ring or a pendant. See all our blue zircon


4.56 ct Orange Red Zircon from Tanzania  [SOLD]

Most natural untreated zircon is brownish in color, But in addition to the rare reds, there are some vivid orange and orange-red colors. This 4.56 ct oval from Tanzania is a nice example. Clean and brilliant, this gem would make an excellent ring. See all our our honey, red and orange zircon.

News from AJS and the Gems World

  • AJS Gems will be exhibiting at the Tucson gem show, Jan 31st to Feb 5th. You can see us at the GJX show in the ICA section, booth #2300.

  • There continues to be a flow of very positive news from Burma. The government followed through on their promise to release a large number of political prisoners, and the US responded by restoring diplomatic relations between the two countries. The EU announced the lifting of some sanctions that prevented Burmese government officials from traveling to the EU. If transparent elections go ahead as planned on April 1st, we can expect further easing by the international community. We can now start to think seriously again about the prospects for free trade in Burmese gems.

  • Sometimes we need a reminder about the difference between minerals and gemstones. There was a good reminder this past month when a purported 57,500 carat faceted emerald was put up for auction in Canada by a gem dealer from Calgary. The 11.5 kg opaque stone was said to be mined in Brazil and cut in India. It was offered at auction as the world's largest emerald, with an asking price of $1.15 million. The stone had not been certified by any reputable gemological lab, and the Canadian gemologist who examined it described it as "treated emerald." Sceptics suspected that it was just dyed white beryl. As things turned out, the gem dealer was arrested by the Royal Canadian Mounted Police on unrelated fraud charges just before the auction, and there were no bids on the alleged emerald.


Ask the Gem Experts

Each month we answer questions from our customers. We welcome your questions and you can submit a question from our contact page.


What does "eye clean" mean exactly? Should I be looking for a higher clarity grade or is eye clean good enough?

Clarity standards for colored gems are quite different than those for diamonds. Almost all natural colored gemstones have some inclusions, and some varieties, such as emerald, rubellite tourmaline and sphene. tend to have significant inclusions. We use the term "eye clean" to indicate when inclusions cannot be seen by the naked eye, and this is considered a high quality standard in the colored gems business. We do have many gems in our collection that we've graded "loupe clean" or "almost loupe clean," but an "eye clean" gem will always yield excellent results when set in jewelry.


I see you offer gem certificates from GRS. Are these certificates recognized internationally? 

GRS or GemResearch Swisslab, is one of the leading gemological labs in the world. Founded by Dr. A Peretti, a well known research gemologist from Switzerland, GRS now has branches in Bangkok, Hong Kong and Colombo. The GRS test reports are highly regarded by gem dealers around the world, and GRS certification is now used extensively by auction houses such as Sotheby's and Christie's. So the GRS lab is in the same class as GIA (Gemological Institute of America), AGL (American Gemsological Laboratories) and the Gubelin Gem Lab.


All the best in gems,

Arnold, Rung & Ron