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Roger Weller, geology instructor            regional geology  planetary  gems

by Mary Lugo
Physical Geology
Spring 2008

Journey with Tanzanite


Considered to be the gemstone of our generation, Tanzanite is taking the world by storm.  A thousand times rarer than a diamond, tanzanite is mined in only one place in the world where new diamond deposits are discovered nearly every month.  Found in the Merelani foothills of Mount Kilimanjaro, Tanzanite was discovered by the rest of the world in 1967.  Tanzanians had long discovered this beautiful stone but decided to keep its beauty to themselves. This gemstone was discovered by a tailor named Manuel d’Souza.  While searching for Rubies d’Souza was led to the deposit of blue stones, by tribesman.  Campbell R. Bridge (Tiffany & CO. employee) was the first person to bring Tanzanite to the United States.  Tanzanite was the given name that Tiffany & CO. gave to the blue Zoisite.

photo by:




Legend has it a lightening bolt struck the ground causing a grass fire.   The heat from the grass fire caused the Zoisite to change to a violet, blue color, and was discovered by a herdsman.  Heat created by a grassfire is not strong enough to change the color of Zoisite, but heating treatments are used in the color change process.  First Generation miners placed the gemstones into charcoal fires to change the color.  Today heat treatments are used to lighten, darken or alter color of gemstones.  Tanzanite can be heated to a temperature ranging from 500ºC - 620°C (932°F).  Tanzanite is usually a yellow, brownish color when mined.  A thermal shock is needed to change the color of the gemstone.  This gem, once changed, encompasses the majestic purple mountains being covered with the evening blue skies.  Tanzanite is a color changing gemstone.  Incandescent (candle light)  lighting causes the purples, lavenders, lilacs, and periwinkles to shine, but when placed in the sunlight the many shades of blues will shine.  “Tanzanite is a gemstone that would not be available in commercial quantities if it wasn’t heat treated” (Guides to Gems and Jewelry).  Thermal heating of gemstones is widely accepted as natural or genuine and not lab created or simulated.





Photos © - Tanzanite One Ltd




                                                        Photo by

The mining of Tanzanite is no easy job with many obstacles stand in the way.  Using outdated techniques miners spend the whole day in the mines with little to show at days end.  The Rainy seasons creates flooding in the mines slowing down the mining of the gemstones even more.  Flooding also causes untimely deaths of the miners.  The mines are broken down into four active blocks lettering A through D.  Some of the blocks are well known. Blocks A and C are reserved for foreign investment.  The C block produced the largest crystal in the world and is the largest producer of Tanzanite out of all the blocks.  D block produces the best quality and color of tanzanite.  Gems TV refers to the Tanzanite from the D block as “AAA- Tanzanite”.


 TanzaniteOne Mine Photos            


            Left, is the worlds largest crystal found 16,839 carats and measures 22cm at its’ widest point. Both Photos show largest single rough stones found to date.(Gemstones & Jewelry)



Manuel d'Souza and TanzaniteOne C-Block Mine

Photos © - Tanzanite One Ltd.                                            Lay out of C block



Tanzanite - Orthorhombic Crystal System 

           Tanzanite is a blueish-purple gemstone variety of the mineral zoisite, which is a calcium aluminium hydroxy sorosilicate belonging to the epidote group of minerals. Tanzanite has a hardness of 6 to 6 1/2 on the Mohs scale. The Toughness of Tanzanite is Poor to Fair. Tanzanite is in the orthorhombic crystal system, with a "bladed" crystal habit. Tanzanite has a refractive index of 1.691.  (Gemstones & Jewelry)

Fun Facts of Tanzanite

-             Tanzanite was used in the movie Titanic for coveted blue jewel

-         2002 Tanzanite was added to Decembers birthstone (which was the first time the list has changed since 1912)

-         Masai chief gave Tanzanite to wives on the birth of their children.   Today the gem is given to mothers on the birth of their first child.



Gavin Linsell.  Guides to Gems & Jewelry. Published by Gems TV holding Limited.

Gems hut.

Diamonds & Gemstones.

 “Something new about Tanzanite”.   Swala Gem Traders.