Tanzanite
Encyclopedia
Tanzanite is the blue/purple variety of the mineral
zoisite
(a calcium aluminium hydroxy silicate
) which was discovered in the Mererani Hills of Northern Tanzania
in 1967, near the city of Arusha
and Mount Kilimanjaro
. It is used as a gemstone
. Tanzanite is noted for its remarkably strong trichroism, appearing alternately sapphire blue, violet and burgundy depending on crystal
orientation. Tanzanite can also appear differently when viewed under alternate lighting conditions. The blues appear more evident when subjected to fluorescent light and the violet hues can be seen readily when viewed under incandescent illumination.
Tanzanite in its rough state is usually a reddish brown color. It requires artificial heat treatment to 600 °C in a gemological oven to bring out the blue violet of the stone. Tanzanite is a rare gem. It is found mostly in the foothills of Mount Kilimanjaro
. The mineral is named after Tanzania, the country in which it was discovered.
, who wanted to capitalize on the rarity of the gem, then only found in Tanzania, but who thought that "blue zoisite" (which might be pronounced like "blue suicide
") wouldn't sell well. From 1967 to 1972, an estimated two million carats of tanzanite were mined in Tanzania before the mines were nationalized by the Tanzanian government.
(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.
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 five 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-ever tanzanite crystal was found in the C-Block mine. The crystal weighs 16,839 carats (3.4 kg) and measures 8.7 in x 3.1 in x 2.8 in (22 cm × 8 cm × 7 cm).
The mining of tanzanite nets the Tanzanian government approximately US$20 million annually. The finished gems are sold mostly on the US market: sales total approximately US$500 million annually.
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.
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 20/20 vision). 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.
' rather than 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 is heat treated in a furnace with a temperature between 550 and 700 degrees Celsius. It should not have any cracks or bubbles in it, as it could shatter or the cracks/ bubble will increase in size.
Mineral
A mineral is a naturally occurring solid chemical substance formed through biogeochemical processes, having characteristic chemical composition, highly ordered atomic structure, and specific physical properties. By comparison, a rock is an aggregate of minerals and/or mineraloids and does not...
zoisite
Zoisite
Zoisite is a calcium aluminium hydroxy sorosilicate belonging to the epidote group of minerals. Its chemical formula is Ca2Al3O...
(a calcium aluminium hydroxy silicate
Silicate minerals
The silicate minerals make up the largest and most important class of rock-forming minerals, constituting approximately 90 percent of the crust of the Earth. They are classified based on the structure of their silicate group...
) which was discovered in the Mererani Hills of Northern Tanzania
Tanzania
The United Republic of Tanzania is a country in East Africa bordered by Kenya and Uganda to the north, Rwanda, Burundi, and the Democratic Republic of the Congo to the west, and Zambia, Malawi, and Mozambique to the south. The country's eastern borders lie on the Indian Ocean.Tanzania is a state...
in 1967, near the city of Arusha
Arusha
Arusha is a city in northern Tanzania. It is the capital of the Arusha Region, which claims a population of 1,288,088, including 281,608 for the Arusha District . Arusha is surrounded by some of Africa's most famous landscapes and national parks...
and Mount Kilimanjaro
Mount Kilimanjaro
Kilimanjaro, with its three volcanic cones, Kibo, Mawenzi, and Shira, is a dormant volcano in Kilimanjaro National Park, Tanzania and the highest mountain in Africa at above sea level .-Geology:...
. It is used as a gemstone
Gemstone
A gemstone or gem is a piece of mineral, which, in cut and polished form, is used to make jewelry or other adornments...
. Tanzanite is noted for its remarkably strong trichroism, appearing alternately sapphire blue, violet and burgundy depending on crystal
Crystal
A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is known as crystallography...
orientation. Tanzanite can also appear differently when viewed under alternate lighting conditions. The blues appear more evident when subjected to fluorescent light and the violet hues can be seen readily when viewed under incandescent illumination.
Tanzanite in its rough state is usually a reddish brown color. It requires artificial heat treatment to 600 °C in a gemological oven to bring out the blue violet of the stone. Tanzanite is a rare gem. It is found mostly in the foothills of Mount Kilimanjaro
Mount Kilimanjaro
Kilimanjaro, with its three volcanic cones, Kibo, Mawenzi, and Shira, is a dormant volcano in Kilimanjaro National Park, Tanzania and the highest mountain in Africa at above sea level .-Geology:...
. The mineral is named after Tanzania, the country in which it was discovered.
Commercial history
Officially called "blue zoisite" it was marketed as tanzanite by Tiffany & Co.Tiffany & Co.
Tiffany & Co. is an American jewelry and silverware company. As part of its branding, the company is strongly associated with its Tiffany Blue , which is a registered trademark.- History :...
, who wanted to capitalize on the rarity of the gem, then only found in Tanzania, but who thought that "blue zoisite" (which might be pronounced like "blue suicide
Suicide
Suicide is the act of intentionally causing one's own death. Suicide is often committed out of despair or attributed to some underlying mental disorder, such as depression, bipolar disorder, schizophrenia, alcoholism, or drug abuse...
") wouldn't sell well. From 1967 to 1972, an estimated two million carats of tanzanite were mined in Tanzania before the mines were nationalized by the Tanzanian government.
World's largest tanzanite
The world's largest faceted tanzanite is 737.81 carats. One of the most famous large tanzanites (242 carats) is the "Queen of Kilimanjaro". It is set in a tiara and accented with 803 brilliant cut tsavorite garnets and 913 brilliant cut diamonds. Because tanzanite is relatively soft, it is usually set in necklaces and earrings, so the tiara is truly a rarity. The tiara is currently on display in the Gallery of Gold and Gems at the Royal Ontario Museum in Toronto, Ontario, Canada. The exhibition is from the private collection of Michael Scott, the first CEO of Apple Computers.Recent developments
In June 2003, the Tanzanian government introduced legislation banning the export of unprocessed tanzanite to IndiaIndia
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
(like many gemstones, most tanzanite is cut in Jaipur
Jaipur
Jaipur , also popularly known as the Pink City, is the capital and largest city of the Indian state of Rajasthan. Founded on 18 November 1727 by Maharaja Sawai Jai Singh II, the ruler of Amber, the city today has a population of more than 3.1 million....
). 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.
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 five 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-ever tanzanite crystal was found in the C-Block mine. The crystal weighs 16,839 carats (3.4 kg) and measures 8.7 in x 3.1 in x 2.8 in (22 cm × 8 cm × 7 cm).
The mining of tanzanite nets the Tanzanian government approximately US$20 million annually. The finished gems are sold mostly on the US market: sales total approximately US$500 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.
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 20/20 vision). 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.
Heat treatment
Excepting stones 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-violet to violetish-blue. Since heat treatment is universal, it has no effect on price, and finished gems are assumed to be heat-treated. Tanzanite is sometimes found in other colors, such as green, although technically it would be called 'green zoisiteZoisite
Zoisite is a calcium aluminium hydroxy sorosilicate belonging to the epidote group of minerals. Its chemical formula is Ca2Al3O...
' rather than 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 is heat treated in a furnace with a temperature between 550 and 700 degrees Celsius. It should not have any cracks or bubbles in it, as it could shatter or the cracks/ bubble will increase in size.
External links
- Time Article of 2007 about the popularity of tanzanite.
- 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".
- The ICA's tanzanite information page.
- Gem Slaves - a short film from 2006 on tanzanite's child miners