Home > Tanzanite
 | | | |
Learn more about "Tanzanite"
|
|
|
Tanzanite{{Infobox mineral
| name = Tanzanite
| category = Mineral Variety
| boxwidth =
| boxbgcolor =
| image = Tanzanite cut.jpg
| caption = Tanzanite gemstone, featuring an oval mixed cut
| formula = (Ca2Al3(SiO4)(Si2O7)O(OH))
| color = Purple to Blue
| habit = Crystals flattened in an acicular manner, may be fibrously curved
| system = Orthorhombic
| twinning =
| cleavage = Perfect {010} imperfect {100}
| fracture = Uneven to conchoidal
| mohs = 6.5
| luster = Vitreous, pearly on cleavage surfaces
| refractive = 1.69-1.70
| opticalprop = biaxial positive
| birefringence = 0.006-0.018
| pleochroism = Present, dichroism or trichroism depending on color.
| streak = White or colorless
| gravity = 3.10-3.38
| Density =
| fusibility =
| diagnostic =
| solubility =
| diaphaneity =
| other = only found in Tanzania
}}
Tanzanite is the blue/purple variety of the mineral zoisite which was discovered in the Meralani (Merelani) Hills of Northern Tanzania in 1967, near the city of Arusha. It is a popular and valuable gemstone when cut. Tanzanite is noted for its remarkably strong trichroism, appearing alternately sapphire blue, violet, and burgundy depending on crystal orientation.
Tanzanite in its rough state is usually a reddish brown color. And as such is heated to 600 °C in a gemological oven to bring out the classic blue violet of the stone.
Commercial history
Manuel de Souza, a Goan tailor and part-time gold prospector living in Arusha (Tanzania), found transparent fragments of vivid blue and blue-purple gem crystals on a ridge near Mererani, some 40 km southeast of Arusha. He decided that the mineral was olivine (peridot) but quickly realized that it was not, so he took to calling it "dumortierite", a blue non-gem mineral. Shortly thereafter, de Souza showed the stones to John Saul, a Nairobi-based consulting geologist and gemstone wholesaler who was then mining aquamarine in the region around Mount Kenya. Saul, with a Ph.D. from M.I.T., who later discovered the famous ruby deposits in the Tsavo area of Kenya, eliminated dumortierite and cordierite as possible I.D.s and sent samples to his father, Hyman Saul, vice president at Saks Fifth Avenue in New York. Hyman Saul brought the samples across the street to the Gemological Institute of America who correctly identified the new gem as a variety of the mineral zoisite. Correct identification was also made by mineralogists at Harvard, the British Museum and Heidelberg University, but the very first person to get the identification right was Ian McCloud, a Tanzanian government geologist based in Dodoma.
Alleged Terrorist Links
On 16 November 2001, in the wake of the September 11, 2001 attacks, a front-page ''Wall Street Journal'' (WSJ) article by Daniel Pearl and Robert Block alleged that significant al-Qaeda funding was generated through illicit trade in tanzanite.
While the story was quickly denounced by many tanzanite dealers,[Weldon, Robert. (2001-11-19.) "No Tanzanite Al Qaeda Link, Say Dealers." ''PJM: Professional Jeweler Magazine'', via professionaljeweler.com. Retrieved on 2007-09-30.] information from the story was widely reported in other media sources. Michael Nunn, president of South African gem company and leading tanzanite mining firm Afgem, dismissed WSJ's article as an unsubstantiated report.[Block, Robert. (2002-02-10.) "Tanzania Unveils Measures to Keep
Tanzanite From Funding Terrorism." ''Wall Street Journal Online''. Retrieved on 2007-10-01.][Zimmerman, Ann. (2002-05-07.)
"Zale to Resume Tanzanite Sales
After Establishment of Protocol." ''Wall Street Journal Online''. Retrieved on 2007-10-01.] Tanzanian officials reported a 70% decline in industry and miner earnings.[Stauffer, Thomas. (2002-2-10.) "U.S. clears tanzanite of terrorist connection" ''Arizona Daily Sun''. Retrieved on 2008-3-27] Tanzanian officials also announced police sweeps to remove illegal miners, and a plan to track gems from miners to traders to retailers.Recent developments
In June 2003, the Tanzanian government introduced legislation banning the export of unprocessed tanzanite to India (like many gemstones, most tanzanite is cut in Jaipur). The ban has been rationalized as an attempt to spur development of local processing facilities, thereby boosting the economy and recouping profits. This ban was phased in over the next two years, until which time only stones over 0.5 grams were affected.
This is a serious situation for the city of Jaipur, as one-third of its annual gem exports are of tanzanite. Some members of the industry fear the ban will set a precedent, leading Tanzania to ban the export of ''all'' raw gem material, including the country's production of tsavorite, diamond and ruby.
In April 2005, a company called TanzaniteOne Ltd. publicly announced that they had taken control of the portion of the tanzanite deposit known as "C-Block" (the main deposit is divided into 5 blocks). Prices for rough material on the open market have increased steadily for the last several years as the company has solidified its control of the market. In August 2005 the largest tanzanite crystal was found in the C-Block mine. The crystal weighs 16,839 carat (mass)|carats (3.4 kg) and measures 22cm x 8cm x 7cm.
The mining of tanzanite nets the Government of Tanzania|Tanzanian government approximately USD20 million annually. The finished gems later being sold mostly on the US market for sales totaling approximately USD500 million annually.
Factors Affecting Value: Grading
There is no universally accepted method of grading colored gemstones. TanzaniteOne, a major commercial player in the tanzanite market, through its no-profit subsidiary, The Tanzanite Foundation, has introduced its own color grading system. The new system's color-grading scales divide tanzanite colors into a range of hues, between blue violet and violet blue.
The normal primary and secondary hues in tanzanite are blue and purple not violet. Purple is a modified spectral hue that lies halfway between red and blue. Tanzanite is a trichroic gemstone, meaning that light that enters the stone is divided into three sections each containing a portion of the visible spectrum. After heating, tanzanite becomes dichroic. The dichroic colors are red and blue. The hue range of tanzanite is blue-purple to purple-blue.[Wise, Richard W., Secrets Of The Gem Trade, The Connoisseur's Guide To Precious Gemstones, p.220]
Clarity grading in colored gemstones is based on the eye-clean standard, that is, a gem is considered flawless if no inclusions are visible with the unaided eye (assuming 20x20 vision).[Wise, Richard W., Secrets Of The Gem Trade, The Connoisseur's Guide To Precious Gemstones, p.35] The Gemological Institute of America classifies tanzanite as a Type I gemstone, meaning it is normally eye-flawless. Gems with eye-visible inclusions will be traded at deep discounts.
Tanzanite Is Heat Treated
Excepting a few stones that were found close to the surface in the early days of the discovery, Tanzanite is universally heat treated to produce a range of hues between bluish-purple to purplish-blue. Since heat treatment is universal, it has no effect on price, and finished gems are assumed to be heat treated. Rarely, tanzanite is found in other colors, green being the rarest, although technically it would be called 'green zoisite' rather than tanzanite.[ GIA On Tanzanite 1999 GIA's short reference list on Tanzanite] Tanzanite may be subjected to other forms of treatment as well. Recently coated Tanzanites were discovered and tested by the AGTA and AGL laboratories. A thin layer of coatings was applied to improve the color of the Tanzanite.[ Tanzanite Coating Farlang's/Gem and Diamond Foundation reporting on AGTA and AGL tests ]
Simulants
A lab-created simulant of tanzanite is called ''tanzanique''. It closely mimics the color of natural tanzanite however it does not display the same pleochroism. Tanzanite is the mineral zoisite, while tanzanique is fosterite. Several different hues of cubic zirconia have also recently come into general use as tanzanite simulants. A popular hue is a medium-light periwinkle blue/lavender color. Another is a deeper purplish-blue. New hue varieties will likely be developed, or at least, the existing ones will become more widely available, as the supply of tanzanite depletes over time and public awareness and interest in the gem grows.
References
External links
- http://www.time.com/time/magazine/article/0,9171,1594137-1,00.html Time Article of 2007 about the popularity of tanzanite.
- http://www.time.com/time/magazine/article/0,9171,900582,00.html Article in the early stages of tanzanite (1969)
- Interesting article and documents from the early days: "Something new out of Africa but no one knew what it was".
- http://www.gemstone.org/gem-by-gem/english/tanzanite.html The ICA's tanzanite information page.
Category:Gemstones
Category:Sorosilicates
Related Images- A rough sample of tanzanite.
Sources: StartLearningNow, Wikipedia | Usage license: GNU FDL
 |
Welcome to Start Learning Now.
Explore to your heart's content, and we hope you enjoy reading the material we
have assembled for you here! |
 |
| | | | |
Related News
|
|
Further Resources
|
|
Related Resources
search
|
|
