December 7, 2017
By Lauriane Lognay
Considered rarer than diamond, tanzanite has been known for its rich blue to purplish colour range since its discovery in 1967. It remains one of the most sought-after gemstones in the industry, and can only be found in Tanzania near Mount Kilimanjaro. As tanzanite celebrates 50 years, let’s dive into the story behind it and how to take care of it for years to come.
About the gem
Although tanzanite is a relatively new gemstone—at least in comparison to lapis lazuli, for example, which was around in ancient Egypt—it is the main gem representing those born in December. The blue/purple gemstone is a variety of the mineral zoisite, which can be found in a multitude of colours, such as yellow, pink, green, and bicolours.
Having a hardness of 6.5 on the Mohs scale, blue zoisite is a relatively soft stone. It is also one of the rarest gems on the planet. It can often be confused with sapphire when the blue is saturated enough—however, most rough gems coming out of the mine are brown. Brown zoisite is mined and then heated to produce the blue and purple hues we see. Natural blue tanzanite is possible, but very scarce.
There is a simple test to determine if a tanzanite was heated or not, which is viable if you don’t have instruments with you (and if the specimen you have in your hands decides to co-operate with you). Natural tanzanite has what is called ‘pleochroism’ in gemmological jargon. Simply put, this is the ability of the stone/crystal to show different colours when viewed from different directions or angles. What is rare about Tanzanite is that it is trichroic (i.e. three-colour).
Most gemstones would not have any pleochroism, or would be dichroic and show only two different colours, but natural unheated tanzanites show three different colours at all times: blue in one direction, purple in another, and a third colour (generally magenta, green, brown, yellow, or a mixture of these). When the tanzanite is heated, the third colour disappears, and only the blue and purple are visible. Tanzanite is one of the few gemstones that can be trichroic or dichroic, making it easier to identify than some other gemstones.
It is said the geology in which tanzanite was born was little short of a miracle, and the Tanzanite Foundation estimates the chance of the same geological phenomenon occurring elsewhere in the world is one in a million. This means the tanzanite mine is the only one in the world and probably always will be, making the gem all the more precious. The gemstone was scientifically called blue zoisite at the time of its discovery, until Tiffany & Co. decided to commercialize it and make it famous by naming it tanzanite. The company decided the name was more ‘sellable’ than blue zoisite.
The tanzanite mine is divided into blocks lettered A through D, with Blocks B and D reserved for the local miners. In 2005, Block C was bought from a company named Tanzanite One, which discovered the biggest tanzanite to date—a magnificent rough weighing 16,839 carats. Tanzanite One also came up with an easy-to-use grading system for tanzanites in the market, which can be found online.
Most of the blue gemstones found in the early days of the mine were said to have been coloured by a wildfire in the area, which heated them naturally if they were close to the surface. The mineral zoisite was discovered in 1805—long before the blue variety was encountered—and can be found in different colours in countries such as Australia and Namibia, but at the time of this writing, the blue variety called tanzanite can still only be found in Tanzania near Arusha.
As mentioned, most tanzanite gems are heat treated as soon as they are out of the mine. The treatment is considered normal and does not have any effect on the gem’s value (though if a natural unheated blue tanzanite is found, that drives the price higher on the market, as with sapphire and rubies).
Tanzanites are not known to be subjected to other treatments—another reason the gem is appreciated in the market. Though there are a few exceptions, they are rare and often disclosed with the sale.
To date, there are no known synthetic tanzanites on the market. ‘Synthetic’ refers to a lab-grown gemstone with the same chemical composition and properties as a natural one. However, tanzanite is often confused with synthetic purple sapphire, cubic zirconium (CZ), and iolite (a purplish brown or colourless gemstone that is also one of the few exhibiting pleochroism). There are other imitations on the market that are far less known, but if you have any doubt, the best option would be to go to your local gemmologist or send the gem to a lab to have it analyzed. You can never be too sure!
Taking care of your tanzanite
With its 6.5 in hardness on the Mohs scale, tanzanite is a lot more fragile than sapphires or rubies and requires careful handling and cleaning. Ultrasonic cleaning is not advisable, but you can soak tanzanite gems in lukewarm water, wash them with soap, and wipe them off with a cloth. A sudden change of temperature or strong heat can be a detriment to your tanzanite, running the risk of changing its colour as well as breaking it—avoid soldering a ring with one at all costs. If you must do so, be very careful not to heat the stone too much. Even with a lot of precaution, tanzanite will develop abrasions over time, which is why most jewellers recommend consumers not wear a tanzanite ring every day or for sports or outdoor activities. With this in mind, you’re all set (or the tanzanite is).
The gemstone of a generation
Visitors to the mine are told by the mining company that tanzanite is the gemstone of our generation. Why? Given there is only one mine, and that mine will one day run out of gems, tanzanite is estimated to only be available for one generation, and future generations will only have old tanzanites on the market. In other words, it’s a good time to buy some! When the mine actually runs out, you can proudly say you were the first owner of that stone (and watch as the prices go up). Even today, scientists have no idea how to find a new source for this gem as they do for diamonds. Tanzanite truly is a miracle of nature.
Lauriane Lognay is a fellow of the Gemmological Association of Great Britain (FGA), and has won several awards. She is a gemstone dealer working with jewellers to help them decide on the best stones for their designs. Lognay is the owner of Rippana Inc., a Montréal-based company working internationally in coloured gemstones, lapidary, and jewellery services. She can be contacted via e-mail at firstname.lastname@example.org.
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