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Encyclopedia > Tanzanite
Tanzanite

Tanzanite gemstone, featuring an oval mixed cut
General
Category Mineral Variety
Chemical formula (Ca2Al3(SiO4)(Si2O7)O(OH)
Identification
Color Purple to Blue
Crystal habit Crystals flattened in an acicular manner, may be fibrously curved
Crystal system Orthorhombic
Cleavage Perfect {010} imperfect {100}
Fracture Uneven to conchoidal
Mohs Scale hardness 6.5
Luster Vitreous, pearly on cleavage surfaces
Refractive index 1.69-1.70
Optical Properties biaxial positive
Birefringence 0.006-0.018
Pleochroism Present, dichroism or trichroism depending on color.
Streak White or colorless
Specific gravity 3.10-3.38

Tanzanite is the blue/purple variety of the mineral zoisite 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. Image File history File linksMetadata Tanzanite_cut. ... This article or section does not cite any references or sources. ... In mineralogy, shape and size give rise to descriptive terms applied to the typical appearance, or habit of crystals. ... A crystal system is a category of space groups, which characterize symmetry of structures in three dimensions with translational symmetry in three directions, having a discrete class of point groups. ... In crystallography, the orthorhombic crystal system is one of the 7 lattice point groups. ... Cleavage, in mineralogy, is the tendency of crystalline materials to split along definite planes, creating smooth surfaces, of which there are several named types: Basal cleavage: cleavage parallel to the base of a crystal, or to the plane of the lateral axes. ... For fractures in geologic formations, see Rock fracture. ... Mohs scale of mineral hardness characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer. ... Lustre (American English: luster) is a description of the way light interacts with the surface of a crystal, rock or mineral. ... The refractive index (or index of refraction) of a medium is a measure for how much the speed of light (or other waves such as sound waves) is reduced inside the medium. ... A calcite crystal laid upon a paper with some letters showing the double refraction Birefringence, or double refraction, is the decomposition of a ray of light into two rays (the ordinary ray and the extraordinary ray) when it passes through certain types of material, such as calcite crystals, depending on... Pleochroism is an optical phenomenon where due to double refraction of light by a colored gem or crystal, the light is divided into two paths which are polarized at a 90° angle to each other. ... In optics, the term dichroic has two related but distinct meanings. ... Pleochroism is an optical phenomenon where due to double refraction of light by a colored gem or crystal, the light is divided into two paths which are polarized at a 90° angle to each other. ... The streak (also called powder color) of a mineral is the color of the powder produced when it is dragged across a unweathered surface. ... Relative density (also known as specific gravity) is a measure of the density of a material. ... Minerals are natural compounds formed through geological processes. ... This article is about the mineral named zoisite. ... Arusha is a city in northern Tanzania. ... A selection of gemstone pebbles made by tumbling rough rock with abrasive grit, in a rotating drum. ... Pleochroism is an optical phenomenon where due to double refraction of light by a colored gem or crystal, the light is divided into two paths which are polarized at a 90° angle to each other. ... CRYSTAL is a quantum chemistry ab initio program, designed primarily for calculations on crystals (3 dimensions), slabs (2 dimensions) and polymers (1 dimension) using translational symmetry, but it can be used for single molecules. ...

Contents

Background

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 outside of a Tiffany & Co. ...


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. Wikibooks has more about this subject: Marketing Look up marketing in Wiktionary, the free dictionary. ... Tanzanias president and National Assembly members are elected concurrently by direct popular vote for 5-year terms. ... The United States dollar is the official currency of the United States. ...


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.

Natural tanzanite cut and set into a bracelet.
Natural tanzanite cut and set into a bracelet.

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. Image File history File links Tanzanitebracelet. ... Image File history File links Tanzanitebracelet. ... Legislation (or statutory law) is law which has been promulgated (or enacted) by a legislature or other governing body. ... , Jaipur   (Hindi: जयपुर, Urdu: جے پور), also popularly known as the Pink City, historically sometimes rendered as Jeypore, is the capital of Rajasthan state, India. ... This article or section does not cite any references or sources. ... BIC pen cap, about 1 gram. ...


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. Tsavorite or tsavolite is a variety of the garnet group species grossular, a calcium-aluminium garnet with the formula Ca3Al2Si3O12)[2] Trace amounts of vanadium or chromium provide the green color. ... This article is about the gemstone. ... Ruby is a red gemstone. ...


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. De Beers was founded in South Africa in 1888 and today comprises rough diamond exploration, mining and trading companies. ... The carat is a unit of mass used for gems, and equals 200 milligrams or 3. ...

A rough sample of tanzanite.
A rough sample of tanzanite.

Image File history File linksMetadata Tansanit_nature. ... Image File history File linksMetadata Tansanit_nature. ...

Prices

The prices of Tanzanite have historically been volatile but the Sighteholder system is keeping prices firm .Retail prices for top quality Tanzanites were just $225 per carat in the year 2000 [1], to $500 in early 2007 [2] and have risen to up to $700 per carat as of May 2007 (Following a 20% rise [3]) partially due to an illegal 350m mineshaft that tapped into Afgem's mine in Tanzania. [[4]]


Many people now are marketing Tanzanite as an investment as the gem is unique to Tanzania and supply is limited.[5] Estimates of when the stone will become extinct vary between 10 and 20 years.These are just estimates as increased demand from India and China will be equally as important as production levels of the stone.


How Is Tanzanite Graded

There is as yet no universally accepted method of grading for Tanzanite. TanzaniteOne has intoduced plans to remedy "price distortion." The company, formerly called Afgem, has established the nonprofit Tanzanite Foundation, which has developed a quality-grading system that justifies a wider range of prices.


COLOR. The new system's color-grading scales divide tanzanite colors into two different hues, blue violet and violet blue.


Each has 10 saturation levels - 6 :


1 - Vivid Exceptional. 2 - Vivid 1. 3 - Vivid 2. 4 - Intense 1. 5 - Intense 2. 6 - Fancy 1. 7 - Fancy 2. 8 - Light 1. 9 - Light 2. 10 - Pale.


This grading system is not as yet accepted throughout the trade and the GIA which is the world's most prestigious laboratory uses a different system [6]. The world's most recognised laboratories have yet to reach consensus on terms used for grading Tanzanite although the top gradings on most systems will be similar.


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. Pleochroism is an optical phenomenon where due to double refraction of light by a colored gem or crystal, the light is divided into two paths which are polarized at a 90° angle to each other. ... This article is about the mineral named zoisite. ... Forsterite (Mg2SiO4) is the magnesium rich end-member of the olivine solid-solution series. ... A round brilliant-cut cubic zirconia Cubic zirconia (or CZ) is zirconium oxide (ZrO2), a mineral that is extremely rare in nature but is widely synthesized for use as a diamond simulant. ...


See also

Gem animals. ... Amber jewellery in the form of pendants. ...

References


  Results from FactBites:
 
Tanzanite - Wikipedia, the free encyclopedia (533 words)
Tanzanite is noted for its remarkably strong trichroism, appearing alternately sapphire blue, violet, and sage-green depending on crystal orientation.
Maasai tribesmen discovered Tanzanite in 1967, supposedly after lightning struck and caused a bush fire which heated the raw brown zoisite into the vivid blue-purple.
The name tanzanite was a trade name coined by Tiffany and Co. shortly after the gem's discovery, an obvious allusion to its country of origin.
Tanzanite (369 words)
Tanzanite is a gemstone that is relatively new to the scene and has gained very significant popularity and acclaim as a gem.
Tanzanite is composed of the mineral called zoisite which is calcium-aluminum silicate.
When selecting a tanzanite for inclusion in a piece of jewelry, bear in mind that it is relatively soft as well as being fragile, making it about as easy to injure as an emerald.
  More results at FactBites »

 
 

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