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February 2017 Newsletter
Brilliance and Fire
Zircon is a natural gemstone that is a favorite of gem dealers and collectors, but it is not well known in the retail jewelry market. Indeed, some consumers confuse it with cubic zirconia, a cheap synthetic sold as a diamond simulant.
Natural zircon is valued 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 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.
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.
Blue is the most popular zircon color and fine blue zircon has more sparkle than any other blue stone in the gemstone world. The colors range from light to medium blue, sometimes with a slight greenish secondary hue. Blue zircon is produced by low temperature heating, but only the Cambodian and Burmese zircon will turn blue when heated.
In addition to its impressive fire, 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 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 cuprite haver a higher density.
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.
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 fine Sapphires from our collection, including 2 Pink Sapphires and a Padparadscha.
Click on a photo to see the details for the item.
News from AJS and the Gems World
- Gubelin Opens Gem Lab in New York
Gubelin Gem Lab, one of the leading gemological laboratories in the world, has opened a permanent gem testing lab in New York, at 608 Fifth Avenue. Based in Lucerne, Switzerland since its founding in 1923, Gubelin opened their first overseas lab in Hong Kong in 2010.
- SSEF Lab to Offer Age Dating for Natural Pearls
The Swiss Gemmological Institute (SSEF) has become the first gemological lab to offer carbon-14 dating of pearls as a client service. The age dating can be used to obtain evidence to support a decision whether a pearl is of natural or cultured formation. This is because methods to commercially cultivate pearls from certain mollusc species began only during the 20th century.
Age determination can also support evidence of historic provenance in the case of antique jewelry and iconic natural pearls. It can also be used to identify fraud in cases where, for example, younger pearls are mounted in historical jewelry items, or have been treated so that they appear older than having been farmed during the 20th century.
Ask the Gem ExpertsEach month we answer questions from our customers. We welcome your questions and you can submit a question from our contact page.
Thanks for your interesting article on pink sapphire. But I was wondering, what's the difference between pink sapphire and ruby? Hope that's not a dumb question! NM, USA
It's not a dumb question ... in fact it's a question that sometimes has gem dealers and gem labs scratching their heads. Pink sapphire and ruby are both corundum (aluminum oxide), colored by traces of chromium. Since pink is just a desaturated red, there is a continuum of hues from pink to red. When a corundum is primarily red -- even if pinkish-red -- it is called a ruby in the gem trade. But it means there will be cases where it is a judgement call that could go either way.
I see you offer certification from a number of different gem labs. I'm planning to buy a blue sapphire for an anniversary gift, which lab would you recommend for the certification? PH, Australia
You'll find that many of the blue sapphires in our collection have already been certified by leading labs such as GRS and GIA. If you need a report for any gem which is has not yet been certified, we are glad to obtain a report for you for the cost of the testing. Currently we are mainly using GIA, who offer very high quality reports at a reasonable price with a turnaround time of about 1 week.
All the best in gems,
Arnold, Rung & Ron