The Great Sapphire Comparison

Australian sapphires are mined near Queensland at Anakie. Historically, Australia produces a deep blue gem which is easily recognizable. Colors range from blue to green to yellow, while the parti-color sapphire which Australia is renowned has zones of both yellow and green. Demand for parti-colored gems has increased over the years. The other region to produce the Australian sapphire is Nigeria, according to Seda Gems.

Nigerian sapphires are mined near Guroji in the Taraba State. In fact, Nigeria has a large quantity of low quality sapphires thought to be too small or too included for viewing by industry standards. However, the GIA consulted an Australian miner in 2012 who endorsed the gemstones as the finest he’s seen coming from basalt-type rocks. The comparison between blue sapphires will show similarity of size, of weight, and of identical coloration. This last point has to be made because sapphires exported to Thailand all undergo a patented heat treatment.

One disappointing property of the sapphire products originating from Australia and Nigeria is they do not exhibit luminescence. The orangey-red glow automatically verifies the chemical content of corundum. So, how should this be interpreted? At first glance, one would consider the iron content as too high. Iron has an effect of quenching fluorescence in high enough concentrations.

Iron on the one hand tends to turn the sapphire yellow; chromium on the other hand turns the sapphire red. Since red corundums fluoresce, one reason neither Nigerian nor Australian sapphires fluoresce is their composition lack the requisite chromium. Thus, neither gem may exhibit yellow discoloration caused by a high iron 3+ content — which is to say quenching is not the reason. If we closely look at locations where these sapphires are mined, then a solution might present itself.

The igneous type of sapphire mined in Australia has a high iron content turning the crystal yellowish-green. The Capricorn Sapphire mine near Anakie produces the parti-colored rather than blue sapphire. The New England gemfield by comparison consisted of 100 mines during the sapphire boom of the 1970s. It is said Australia’s best blue sapphires originate from there, NSW. Due to declines in market conditions, only a few of those 100 mines still operate there today. Color zoning is quite common with the “blue on blue”sapphires mined at Reddestone Creek, New South Wales. The average blue sapphire mined at Reddestone Creek were 51.3% aluminum, 47.8% oxygen, 0.85% iron 2+, and 0.02% titanium.

“Pure sapphire is colourless. In the presence of the common impurities iron and titanium, the blue colour is generated by the Fe-Ti charge-transfer. “ [source: Azo Materials; Sapphires - Processing, Grading, Characteristics, Heat Treatment and Marketing of Sapphires; Aug 16 2013]

As far away as West Africa, Nigeria produces a significant number of gemstones. Sapphire mining itself being relatively new, 20 to 30 years. The states of Borno, Taraba, Bauch, and Kaduna receive international loans and government investment to expand mining operations. But, sapphire yields from secondary deposits are dark blue and green and require heat treatment in order to improve their color. Samples taken by the GIA found significant levels of iron with small amounts of titanium: “It is interesting to see that the fine blue color seen here is only produced by an average of 17 ppma of titanium content associated with iron.”

In conclusion, the high iron 2+ content combined with trace titanium produces the blue sapphire’s blue color. This production does not fluoresce because of an absence of the requisite chromium ion. A spot check with a ultraviolet lamp can not rule out the authenticity of a blue sapphire — itself a positive endnote.