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Tanzanite- December’s birthstone

Filed under: Mineral of the day,regular postings — Gary March 27, 2007 @ 7:46 pm

TanzaniteTanzanite_gemTanzanite_rough_2

Tanzanite is the blue/purple variety of the mineral zoisite (Ca2(Al. OH)Al2(SiO4)3) discovered in the Meralani Hills of northern Tanzania in 1967, near the city of Arusha. It is a popular and valuable gemstone when cut, although its durability is somewhat lacking; its tendency to break sometimes precludes appropriate use as a ring stone. Tanzanite is noted for its remarkably strong trichroism, appearing alternately sapphire blue, violet, and sage-green depending on crystal orientation. However, most tanzanite is subjected to artificial heat treatment to improve its colour: this significantly subdues its trichroism.

Background

On July 7, 1967, 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 wasn’t and took to calling it “dumortierite”, a blue non-gem mineral. Shortly after, 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 a 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. Hyman Saul got two of the samples facetted and showed them to Henry Platt of Tiffany and Company, who immediately appreciated the beauty of the gem and subsequently coined the name “tanzanite”, an obvious allusion to its country of origin. These two stones were subsequently mounted in rings.

The allusion to the country was thought necessary in order to make the stone marketable to the public: the name has since stuck as a varietal designation. Tanzanite’s present-day popularity as a gemstone is largely thanks to Tiffany’s marketing campaigns. The mining of tanzanite nets the Tanzanian government approximately USD $20 million annually, the finished gems later being sold mostly on the US market for sales totaling approximately USD $500 million annually.

In October of 2002 the AGTA.org made the first change in more than 90 years to the “modern birthstone chart” and crowned Tanzanite as the December birthstone.

In June of 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). Over the next year, this company established a De Beers-like control over the tanzanite market. The company is also increasing its control of all newly mined tanzanite by purchasing a large portion of the production coming from the operations of the independent miners working in the area. This is the first time that a colored gemstone has been controlled in this way. Prices for rough on the open market has 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 carats (3.4 kg) and measures 22 cm by 8 cm by 7 cm.

Tansanit_rough

In February 2006 TanzaniteOne Ltd. announced that they were moving forward with their marketing strategy to make Tanzanite “the” birthstone. They plan to market the rare gem as a stone one would give a child at birth, to celebrate new life.

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. A periwinkle blue/lavender colored Cubic Zirconia has also recently come into general use as a tanzanite simulant

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