Tanzanite

Tanzanite is the blue to violet variety of the mineral zoisite, a calcium aluminium hydroxy silicate. It is valued for its vivid color and its strong pleochroism, appearing blue, violet, or brownish yellow depending on the crystallographic direction viewed.

Discovered in 1967 in the Mererani Hills of northern Tanzania near Mount Kilimanjaro, tanzanite was introduced to the jewelry trade by Tiffany & Co., which marketed the gem as a flagship product and named it after its Tanzanian origin.

Natural tanzanite typically shows a brownish yellow to brownish hue when unheated. Through controlled heat treatment, usually at 500–700°C, many stones are transformed into vivid blue or violet colors. The color is largely due to trace vanadium and irradiation effects; heating helps stabilize the blue by reducing the brown undertones.

In terms of physical properties, tanzanite has a Mohs hardness of about 6.5–7 and a specific gravity around 3.3. It is relatively durable for a colored gemstone but can be scratched or damaged by sharp blows, and it should be protected from sudden temperature changes and hard impacts.

Today, tanzanite is primarily sourced from the Mererani Hills. It is sold in a range of cuts and sizes and remains a prominent, market-concentrated gemstone associated with Tanzania.