Misconceptions about Blue Zircon

Zircon, and especially Blue Zircon, is one of our favorite gemstones. We have dealt with this gem for over 30 years and have frequently travelled to Cambodia to visit the mines and markets.

While Blue Zircon is still relatively uncommon in the wider jewelry market, we have seen a dramatic increase in popularity, particularly in the US, in the past decade. Interestingly, there appears to be quite a lot of misinformation about this gem within the trade.

Cambodian Blue Zircon (Photo By Thai Lanka Trading)

Blue Zircon from Ratanakiri, Cambodia, before and after heat treatment (Photo By: Prasit Prachagul, Thai Lanka Trading)

Blue Zircon Mine (Photo by Mark H Smith)

‘Cooking’ Blue Zircon (Photo by Mark H. Smith)

Some dealers mistakenly claim their blue zircons are untreated.

This is extremely unlikely, as there has never been any evidence of naturally occurring blue zircon found. The blue color is the result of a very simple heat treatment of brown zircons, from a few very specific localities. Though brown zircon is found in hundreds of localities around the world, the only commercial source of stones that will heat treat to a fine blue, is Ratanakiri province, in northeastern Cambodia. And yet no naturally blue stones are found there.

The area consists of overlapping debris fields of many small volcanic eruptions ranging in age from 700,000-2 million years. Many of these small volcanic debris fields contain zircon and the zircons from some fields will heat treat to a fine blue color and those from other fields will not. The locals know which mining area produces stones that will heat to the best blue. The treatment is simple - the brown stones are double sealed in airtight crucibles and set in a vertical oven atop a pile of charcoal. A blower fans the fire for about an hour and the crucible attains white heat. After a short cooling, the crucible is cracked open and the brown rough has hopefully become various shades of white, pale blue and fine blue.

Brown zircons similar in color to those from Ratanakiri are found all over the world, but only those from a very few sources will change to blue with heat treatment. We have heard that some Nigerian brown zircons can be heated to a very pastel blue, and we have seen some very pale blues attributed to Hainan China. Some zircons found in the old ruby mines along the Thai-Cambodian border can be heated to a light blue, but these are of the same field of volcanism as the Ratanakiri deposits.

There are also misconceptions about when Blue Zircon was first discovered.

We have heard gem marketing ‘experts’ spin stories that blue zircons were the sacred gems of the builders of Angkor Wat a thousand years ago. There is absolutely no support for this as the correct sources and the heat treatment process apparently weren’t discovered until the early 20th century. Max Bauer, in his excellent book Precious Stones Vol II (1904), writes many pages on zircon types, sources and treatments. He discusses the color and specific gravity changes produced by the heating of zircon, but he makes absolutely no mention of blue zircon. The first reliable reference we have to blue zircon is in 1927 by Dr. George Frederick Kunz. In a lecture to the New York Mineralogical Club, of which he was president, he makes reference to “the newly popular Starlite zircon…from the old sapphire workings north of Bangkok”. His geography is a bit shaky but this is the earliest reference we could find to Blue Zircon…so it appears that the process to treat Cambodian brown zircons to blue, was discovered sometime between 1904 (Max Bauer’s book) and 1927 (Dr Kunz’s lecture). We are always eager to learn more about the history of Blue Zircon, so if any reader of this has more detailed information we would love to hear it.

Regardless of the history of the stone, we love the incredibly rich color that Cambodian Zircon can heat to. Blue Zircon, in fine, well-cut, and clean quality, has been one of our specializations for decades and hopefully many more years to come. A beautiful gem.

Blue Zircon (Photo by Thai Lanka Trading)