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Zoisite (var. tanzanite)

Tanzanite (NMNH G10696-00) from the National Gem Collection.
Photo by Ken Larsen. Click to zoom.
Catalog Number NMNH G10696-00
Locality Tanzania
Weight 18.56 ct

Purchased with funds from the Tiffany & Co. Foundation in 2011.

In 1967, violet blue crystals of the mineral zoisite were discovered in the foothills of Mount Kilimanjaro in Tanzania. These intensely colored crystals were extraordinarily beautiful and propelled zoisite into the ranks of the important gem minerals. In 1968, Tiffany & Co. marketed the new zoisite gem under the name of tanzanite, to honor its single-source availability and its East African birthplace. Since its discovery, tanzanite has steadily increased in popularity. The most valuable tanzanite gemstones are a deep sapphire blue color with highlights of intense violet. Tanzanite exhibits the optical phenomenon of pleochroism, appearing intense blue, violet, or red depending on the direction through which the crystal or gem is viewed. Consequently, the predominant hue of a tanzanite gem depends on the orientation in which it is cut and can therefore resemble a sapphire or even an amethyst in color. All tanzanite gemstones originate from the area where they were initially discovered in Tanzania, where they are mined from metamorphosed limestone. This unusual emerald-cut tanzanite gem, faceted by Paul Merkel, weighs 18.56ct and is a deep blue color.

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