Tanzanite: December's Newest Birthstone Is Found in Only One Location on Earth

Said to be rarer than diamond by a factor of 1,000 times, tanzanite is mined in only one location on earth — a 2 km by 4 km swath along the Merelani Hills of Tanzania at the base of Mount Kilimanjaro. The mine's remaining lifespan is less than 30 years.

Tanzanite’s color is an intoxicating mix of blue and purple, unlike any other gemstone. The Gemological Institute of America describes exceptional tanzanites as having an intense violetish-blue color with red flashes of pleochroic color coming from within the stone.

Pleochroism is an optical phenomenon in which a gemstone appears to have different colors when observed at different angles.

The “Petersen Tanzanite Brooch,” shown above, is part of the Smithsonian’s National Gem Collection in Washington, DC. The piece was designed by Harry Winston in 1991 and donated to the museum by Donald E. and Jo A. Petersen in 2002.

The triangular-cut matched tanzanites weigh approximately 30 carats and are adorned by 24 carats of marquise, pear and baguette-cut diamonds in a floral motif. The tanzanite “flowers” may be detached and worn as earrings.

In 2002, a jewelry-industry trade organization — the American Gem Trade Association — designated tanzanite as an official birthstone for the month of December. The occasion was momentous because, up until that point, the list hadn’t been amended since 1912.

A Maasai tribesman named Jumanne Ngoma is credited with discovering a cache of blue-violet gems that, at first glance, appeared to be sapphires. Gemologists would later confirm that Ngoma’s find was a totally unique variation of zoisite.

Samples of the mineral caught the attention of Tiffany & Co., which launched a campaign to market the gems as “tanzanite” to honor its country of origin and the only place on earth where tanzanite can be found. (The name “blue zoisite” was panned by the Tiffany marketing team because it sounded too much like “blue suicide.”)

Credit: Photo by Penland and digitally enhanced by SquareMoose / Smithsonian.