Tanzanite is a rare mineral only found in the Mererani or Merelani hills tanzanite mining area of Tanzania. Located in the Simanjiro district, the Merelani mining area is 16 kilometers south of the Kilimanjaro International Airport, and 70km south-east of Arusha, at the base of Mt. Kilimanjaro.
To this day, the only source of Tanzanite in the world is this several square mile area in the Merelani Hills. This limited supply makes Tanzanite 1000 times more rare than Diamonds. Tanzanite is a newly discovered gemstone and the name "Tanzanite" was established by Tiffany & Co. in 1968.
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.
Tanzanite can sometimes be mistaken for blue sapphire, but tanzanite can have very pronounced pleochroism, which reflects different colors from different angles. "Pleochroism" is an optical phenomenon due to the double refraction of light which is divided into two "polarized" paths at a 90° angle to each other. When viewed from the top or front, tanzanite's hue will appear blue to violet-blue, and when viewed from the back it will appear violet to bluish-purple.
Tanzanite specimens that have a predominantly blue color can be more expensive than purplish-blue varieties, because these crystals tend to form with the blue color axis oriented along the width of the crystal as opposed to its length. Cut orientation is critical to take maximum advantage of the color.
Blue tanzanite obtains its distinct violet-blue color from trace amounts of vanadium and chrome tanzanite (chrome zoisite) obtains its vivid green coloration from its chromium content.
Photos © - Tanzanite One Ltd.
In July 1967, a tailor named Manuel d'Souza (above, left - on left) was prospecting for rubies in Tanzania Africa when a group of Masai tribesmen led him to a deposit of blue stones. Masai legend is that cattle herders first noticed this stone some 30 years previously, after a brush-fire caused by lightning burned large areas of the plains at the base of Mt. Kilimanjaro in Tanzania. The herders noticed that brown Zoisite crystals had turned a deep blue-purple due to the heat from the fire. The entire area soon became covered in mines, and d'Souza was unable to maintain control over his mining claim. In 1971, the Tanzanian government took control of the mines and turned them over to the State Mining Corporation in 1976.
Tanzanite Mining
There are four actively mined tanzanite areas or 'blocks,' that are labeled A through D. The 'A block' and 'C block' were reserved for foreign investment, while B and D can be mined by ingenious locals. In 2005 a privately owned company named Tanzanite One Ltd. took control of Tanzania's largest tanzanite mine known as "C-Block" (above, right). The mine has already reached a depth of 1000 feet and there is growing concern that the supply of Tanzanite could be depleted in a few decades.
Photos © - Tanzanite One Ltd.
Tanzanite One has established De Beers-like control over the tanzanite market by intentionally restricting it's supply and distribution. This is the first colored gemstone that's sales and distribution have been controlled in the way that diamonds have been. The world's largest tanzanite crystal was found in TanzaniteOne's C-Block mine in 2005. The crystal weighed 16,839 carats and measured 22 cm at it's widest point.
Small-Scale (Wana-Apollo) Tanzanite Mining
There are many so called 'small-scale' tanzanite miners within Tanzania (called Wana-Apollo) that employ nomadic workforces in the 100s to conduct exploratory excavations to locate Tanzanite veins in A, B, and D blocks. Once a vein is found, the miners use a system called "Bing," enlisting several groups of Wana-Apollo to assist in exploiting the vein.
There are 430 'plots' that can be mined in the remaining B and D blocks. These non-mechanized miners use daisy-chains of workers to hand excavate the mining shafts. Merelani township is the tanzanite trading center for small-scale meiners.
These photos from the Tanzanite One Ltd. website are of stones found at the C-Block mine and represent some of the largest single rough stones found to date.
Chemical composition: CaA13(O/OH/SiO4)Si207
The natural color of tanzanite (the mineral zoisite), prior to the application of heat, is brown or bronze (see photo, below), which can be especially pronounced when observing the stone on its 'C' axis. Tanzanite that has not been exposed to heat in its natural state can be heat-treated to 500ºC - 620°C (932°F) to produce the deeper blue color that is characteristic of the stone. The heat treated stone has a deep indigo-blue color in natural sunlight, and appears violet in incandescent light.
Synthetic or Simulant Tanzanite
There is a new material on the gem market known as "Tanzanion" which is manufactured in Russian. Tanzanion is a laboratory-created pulled synthetic Forsterite that is a relatively convincing simulant of Tanzanite. Tanzanion shares some of the physical and pleochroic properties of natural tanzanite, with a higher hardness of 7.0. Tanzanion has a refractive index of 1.635 to 1.670 and a specific gravity of 3.24. There is also a YAG simulated tanzanite that is a convincing substitute.
Morion Company - Tanzanion
Solix - Tanzanione
Shree Prakash Gems - Manufactured Tanzanite
