Mgunduzi wa madini Tanzanite afariki dunia". BBC News Swahili (in Swahili) . Retrieved 26 September 2023. Eugenia Sheppard (3 October 1968). Section B. "Inside Fashion: Something new at Tiffany's is Tanzanian blue gem". Durham Morning Herald (finaled.). Durham, N.C.: The Durham Herald Co.: 2B. OCLC 9519676. 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). [29] The Gemological Institute of America classifies tanzanite as a Type I gemstone, meaning it is normally eye-clean. Gems with eye-visible inclusions will be traded at deep discounts. The Tanzanite Foundation". The Tanzanite Foundation. 22 April 2013. Archived from the original on 9 February 2005 . Retrieved 26 November 2013. Tanzanite". Gemstone.org. Archived from the original on 12 September 2008 . Retrieved 29 August 2011.

There is no universally accepted method of grading colored gemstones. TanzaniteOne, a major commercial player in the tanzanite market, through its non-profit subsidiary, the Tanzanite Foundation, [27] has introduced its own color-grading system. [28] The new system's color-grading scales divide tanzanite colors into a range of hues, between bluish-violet, indigo and violetish-blue. There are many accounts of the discovery of tanzanite, but only one recognised by the government of Tanzania. In January 1967, Jumanne Mhero Ngoma (originally from Same District, Kilimanjaro) stumbled upon the sparkling blue stones at the Mererani hills in the Kiteto district of the then Arusha Region (presently Manyara Region). He was issued with a certificate of recognition three years later by the then President Julius Nyerere and a financial reward of Tsh 50,000 for his efforts. In 1984, he was issued with a certificate for scientific discovery by the Tanzania Commission for Science and Technology. [10] [11] Commercial history [ edit ] Craft work on tanzanite Weldon, Robert. "An introduction to gem treatments". gia.edu. Gemological Institute of America, Inc. Briggs, Philip; McIntyre, Chris (2013). Tanzania Safari Guide: With Kilimanjaro, Zanzibar and the Coast. Bradt Travel Guides. p.104. ISBN 978-1-84162-462-4. E. Skalwold. "Pleochroism: trichroism and dichroism in gems". Nordskip.com. Archived from the original on 6 September 2012 . Retrieved 29 August 2011.

The verdict: Vodkas

Coatings: a new Tanzanite treatment uncovered". farlang.com. Farlang's Gem and Diamond Foundation; Gemological Association of Great Britain; German Gemological Association; Netherlands Gemological Laboratory. 25 May 2008.

Cobley, Mark (3 August 2005). "World's Biggest Tanzanite Gem Found Near Kilimanjaro (Update3)". Bloomberg. Archived from the original on 24 September 2015 . Retrieved 31 December 2013.Export ban on tanzanite in Africa leaves Jaipur gems sector in lurch". The Times of India. 3 October 2013. Archived from the original on 29 December 2013 . Retrieved 31 December 2013. Featured gemstone: tanzanite". GIA Library. Gemological Institute of America, Inc. Archived from the original on 13 May 2008. Tanzanite is noted for its remarkably strong trichroism, appearing alternately blue, violet and burgundy depending on crystal orientation. [6] Tanzanite can also appear differently when viewed under different 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. In its rough state tanzanite is colored a reddish brown to clear, and it requires heat treatment to remove the brownish "veil" and bring out the blue violet of the stone. [7] From 1967, an estimated two million carats of tanzanite were mined in Tanzania before the mines were nationalized by the Tanzanian government in 1971. Tanzanite may be subjected to other forms of treatment as well. Recently, coated tanzanites were discovered and tested by the AGTA and AGL laboratories. [34] A thin layer containing cobalt, determined by X-ray fluorescence, had been applied to improve the color. It was noted that "coatings in particular are not considered permanent", and in the United States are required to be disclosed at the point of sale.