Tanzanite is the blue-to-violet variety of the mineral zoisite, and it is one of the rarest gems on Earth for a simple reason: it is found in only one place, a few square kilometers of the Merelani Hills near Mount Kilimanjaro in northern Tanzania. Discovered only in 1967 and named by Tiffany & Co., it went from unknown to one of the world's most popular blue gems in a single generation.
One source, and someday none
Because tanzanite comes from a single small deposit, it is genuinely finite in a way that most gems are not; when the Merelani mines are exhausted, no new commercial source is expected. That scarcity is a core part of its appeal and its marketing. Fine large stones with vivid color are already treasured.
A gem of three colors
Tanzanite is strongly pleochroic, and specifically trichroic: a single rough crystal shows blue, violet, and a brownish or burgundy color depending on the viewing direction. Cutters orient the finished gem to capture the most desirable blue-violet face-up, which is why so much rough is "wasted" and why fine color costs more. The most prized stones show a deep, saturated blue with a violet flash.
Nearly always heated
Almost all tanzanite begins as a brownish or yellowish zoisite in the ground. Gentle heating (around 500–600°C) transforms it to the blue-violet color we know. This treatment is standard, stable, and accepted across the trade; unheated natural-blue tanzanite is rare and mostly of interest to collectors. Assume any tanzanite you buy has been heated.
Beautiful, but wear it wisely
At Mohs 6 to 7 and with distinct cleavage, tanzanite is considerably softer and more fragile than sapphire. It can scratch, and a sharp knock along the cleavage can chip or break it. It is a wonderful stone for pendants and earrings and for occasional-wear rings, but it is not the best choice for an everyday ring exposed to hard knocks.
A modern birthstone
Tanzanite's popularity earned it official status as a December birthstone, added in 2002, the first change to the traditional birthstone list in decades. It joins turquoise and zircon for that month and offers a rich, jewel-toned alternative to them.
Caring for tanzanite
Clean tanzanite with warm soapy water and a soft brush only. Never use ultrasonic or steam cleaners, and avoid sudden temperature changes and household chemicals. Store it separately so harder gems do not scratch it, and choose protective settings for rings. Treated with reasonable care, its blue-violet color is stable and does not fade.
Tanzanite is a genuinely rare, single-source gem with a color few stones can match. Accept that it is heated, respect that it is soft, wear it in protected settings, and it will reward you with one of the most beautiful blues in the gem world.
