Tanzanite is the blue and violet variety of the mineral zoisite (a calcium and aluminum hydroxyl sorbosilicate), produced from small amounts of vanadium. Tanzanite belongs to the group of mineral eduts. Tanzanite is only found in Tanzania, in a very small mining area (about 7 kilometers (4.3 mi) long and 2 kilometers (1.2 mi) wide) near the Mirirani Hills.
Tanzanite is known for its remarkable versatility, appearing alternately blue, violet, and burgundy depending on the orientation of the crystal. Tanzanite can also appear differently when viewed under different lighting conditions. Blue appears most clearly when exposed to fluorescent light and violet tones are easily seen when viewed under incandescent lighting. In its coarse state, tanzanite is colored reddish-brown until clear, and requires heat treatment to remove the brown “veil” and bring the blue violet out of the stone.
Tanzanite was formed about 585 million years ago during the middle of the Ediacaran period by massive plate tectonic activity and intense heat in the area that later became Mount Kilimanjaro. The mineral is located in a relatively complex geological environment. The deposits are usually located at the “joint” of the iso-folds.
In July 1967, Manuel de Sousa, a Goan tailor and part-time gold prospector living in Arusha (Tanzania), found transparent shards of blue-violet gem crystals on a ledge near Merirani, about 40 km (25 mi) south of East Arusha. He assumed the mineral was olivine (aquamarine) but after realizing that it wasn’t, he concluded that it was “domorterite” (an immaterial blue mineral). Shortly thereafter, the stones were offered to John Sol, a Nairobi-based consulting geologist and gem wholesaler, who was then mining aquamarine in the area around Mount Kenya. Saul, who later discovered famous sapphire deposits in the Tsavo region of Kenya, disposed of domorterite and cordierite as possibilities, and sent samples to his father, Hyman Saul, vice president at Saks Fifth Avenue in New York. Hyman Sol 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. The identification was correctly identified by mineralogists at Harvard University, the British Museum and the University of Heidelberg, but the first person to have the correct identification was Ian McCloud, a Tanzanian government geologist based in Dodoma.
In 1990, the Tanzanian government divided tanzanite mines into four sections: squares A, B, C and D were given to large operators, while squares B and D were reserved for local miners. In 2005 the government renewed the lease of the Block C mine to Tanzanite One, which paid US$40 million for the lease and mining license.
In June 2003, the Tanzanian government introduced legislation banning the export of unprocessed tanzanite to India. (Like many gemstones, most tanzanites are cut in Jaipur.) The reason for the ban is to try to stimulate the development of local processing facilities, thus boosting the economy and recovering profits. This ban was gradually implemented over a period of two years, until that time only stones weighing more than 0.5 grams were affected.  In 2010, the government of Tanzania banned the export of coarse stones weighing more than one gram.
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