The Heating of Tanzanite

Posted on March 25th, 2012 in Blog by || No Comment

There is a gemstone that can be found in only one place. This gem is called tanzanite, and it is located in the African nation of Tanzania. It known as one of the rarest, most beautiful gems in the world. Because tanzanite is only exported exclusively from one place, the supply could run out soon, and many people have bought the gem so that they can own it before the supply runs out, when its worth will increase. The fascinating thing about tanzanite that most people do not realize is that its natural color is not the beautiful blue-violet color they love; it is naturally colored in browns, reds, or greens. This is because it is from the zoisite family, and the zoisite is a brown-colored mineral, so many tanzanite gems start out with a brownish color. What happens to make the gem turn from this unappealing color to the vivacious bluish color we see when it is sold in stores, is that it is refined by flame to bring out its beautiful blue hue. It is similar to cutting the rough edges of a diamond, but the only difference is that tanzanite (and all zoisite minerals) are very fragile and have soft stones, so they are susceptible to falling apart easier than other gemstones.

The tanzanite gemstone is treated by heat to a temperature of 550 to 700 degrees Celsius in a gemological oven, and the heat is the thing that draws out the purple-blue/blue-purple color that is seen on the market. There are a variety of tinges and shades within these two hues that tanzanite comes in (after being heat-treated), and the blue gem can turn out to have a little red, green, or grey tinge to it. Furthermore, it can come in either a very transparent or a rich, deep color. The heating process brings out the specific color found in that one particular tanzanite, and that tanzanite can be either a light shade, a medium shade, or a dark shade of blue and/or violet. The heating treatment works in an interesting way:  The natural-colored tanzanite is placed on a kiln (oven) tray, and the tanzanite pieces need to be separated about an inch away from each other and the edges of the tray; the smaller gems are easier to heat than the large pieces. Then, once this is done, the tray is placed in the center of the oven, and the temperature can first be set at a lower level, such as 850 degrees Fahrenheit. Once the oven is heated at this temperature, the temperature then is raised 10 to 15 notches higher to about 930 degrees. The gems are heated for an hour, and if the color has not changed from its unattractive brown to the beautiful blue-purple color, it is placed in the oven again for another 2 to 4 hours. It takes time for the gem to change from its natural form to the one that people desire, but during this time of heating, it will change color for sure. Then the tanzanite will be cooled in a dark, cool place for 24 to 48 hours, and finally it will be ready to be set into jewelry.

Tanzanite is a unique gemstone and has lasting popularity as a result of many factors. First, it can only be found in the country of Tanzania, and this means there is a limited supply, which is why many people buy it—if the supply runs out, the price will rise. Moreover, it is not sold in its original color, but is heat-treated to become a blue-purple, and its vibrant color is a main reason people purchase the gem. In addition, it is one of the   softest and most fragile stones, and this only makes it twice as popular.

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